Basically the generic magic system of SR allows for creativity on the stlye of what your magic looks like. It is an often over looked piece of the game world where we say, "I throw a fireball."
Instead of, "I throw a burning jackalatern that giggles manically before it explodes."

There are several broad trends based on how you want to run your magic that suggests styles for your watcher spirits.

First off is the school method: Where magicains of the same school of magical theory summon the same types of watcher spirits due to their stylistic belief.
For example totemic shamans summon small animals of their totem as vassel spirits. All Renewed Hermetics summon goblinoid fae imps etc

Second personal fiat: You can summon a watcher spirit to look like what ever you want when ever you want, from a small ball of fire to Dali's melting clock face and anything in between.

Third: A mix of the two above styles. Your school gives you a spectrum of selectable types of watcher spirits. A owl shamen chooses that all his watcher spirits will be a specific speicies of owl.

So as a matter of style, what do your watcher spirits look like?

With my Possesion Voodoo priest, my watchers all inhabit a small stick figure broom with Arms. Just as in Disney's the Magicians Apprentice.

Never really get to look at them, it is just too much fun using them as golf balls.

depends on what character i play . . with a cat-shaman, the smaller ones will look like little kittens, the medium kind will look like garfield and the big ones like mean cats . .
i base the whole look and feel of magic on two things: the character and his tradition/totem . .
a hermetics watcher might look like the should devil and angel or something like that . .
a chaos magician with a knack for technology might have them look like little robots or something like that

...I always pictured them as the goofy cartoonish characters. Though I think it was the Grimiore (Grimiore II?) which had an interesting picture of winged eyeballs chasing some dude though an alleyway which I thought looked appropriate.

I always encourage the players to describe spell effects. During play that usually comes into RP affect alot.
One of my last campaigns had a Gothic Victorian England feelign character. Whos mana balls pulled the effect of Pinhead from Hellraiser. (chains with hooks erupting from hidden areas around the place)

As far as spirits go, watcher or otherwise I allow the player to describe watchers and they range from a naked eyeball with wings to a puppydog. Most the time spirits are off the cuff though. SImiliar to hit locations, descriptions for effect.

For some reason, my subconscious insists that they all look like the Pillsbury Dough Boy, and go "teehee" a lot. I blame my mother...

...of course they could always end up looking like the Sta-Puft™ marshmallow man.

When there were still domains and elementals, it was fairly easy to describe them on the fly because they would take on some characteristic of the domain or element.

I can't really get away from the domain concept. I like it. It gives spirits a flavor. Sure, you can just summon anything nearly everywhere now, but whenever spirits get summoned within an interesting domain I give them more personality and sometimes a minor buff for knowing specific things.
Sure it isn't canon anymore, but it is fun to do. As for watchers, the only thing I see them used as is abuse. They are just so utterly useless for anything else now

<------- Like this.

Really though, anything you want (though usually small)

I pretty much have followed a combo of the methods - each tradition has a limited range of watcher forms they summon. I've played characters who summon demonic imp-like watchers, watchers that looked like shadows with nothing casting them, and (waaaay back) the winged eyeballs protrayed in the Grimoire II.

That's not too bad - I once played a mage who's Watcher spirits took the form of Hello Kitty. But... mostly I did that to irk my fellow gamers lol

My gator shaman summons little mini alligators.

That's not that interesting.

But here's the one that hasn't come up - can watchers have personalities, and can you keep calling the same ones over and over again and have relationships with them?

My gator shaman considers Modesty and Chastity his closest companions in the world. They offer him unconditional love. (Yes, he's has some slight social challenges.)

Note that I am not suggesting there be any game bonus effect for this. Nor would I insist that the "resummoned" watchers carry any memories from previous summonings. They might not even be the same ones. There might be no such thing as same ones.

But to my shaman - in his mind - they are always Modesty and Chastity. He figures they are always the same ones cuz they appear as he expects them to, and always act the same (cuz they are watchers, and insofar as they can express an appearance and a personality, they are reflections of his expectations).

Good point.
One of my players has a chaos mage that believes she summons the same watcher spirits and has also taken to naming them accordingly.
In a related concept exploration in game a contact who is a powerful mage has summoned a high force watcher (force six) for a year to see what the long term effects of watcher spirits evolution can be.

Speeking of weird spirit forms, Crackerjack who used to play with us said his Guardian spirits look like Bruce Willis from Die Hard (Yippe Ki-a Mutherfuckers) and his Guidance spirits look like Mr. Miyagi. I forgot what the rest were like.

Watchers can only be force 1?

SR3.

I may be misremembering, but in SR3, aren't Watchers limited to a maximum of Force 3?

My chaos mage's watchers looked like short anthroforms who's entire bodies were obscured in a hooded robe. Vaguely Jaway.

Watchers were summoned for a specified number of hours in 2 (and 3?) ED. That became the Summoning skill target number and the force was something like successes / 2. The only part that confused me was that the drain was based off their Force, which you didn't know until you had summoned it. I thought it was weird. So basically yes, they had a max force of 3 for any sane character. But if you have a Watcher spirit summoning focus thing (i'm not sure WHY you would have one though) you could theoretically have some more successes. If you're lucky I suppose you could eventually get one at force 6, but it would take a decent bit of work. Though, if you DID have watchers at Force 6, they would probably actually be pretty decent. Not really for combat or anything, unless you can have them attack people... but i don't recall that possible... anyone know?

Half Magic I think. This appeared in Street Magic and too late to save cyberzombies from force 9 watchers (More on them later).

Watchers what I have seen

Calico (my Cat wiccan) - The usually appear as fey-cats (various colours some sparklyness)

Timber/Haunches (Both Wolf Shamen) Small wolves (animal mentors thing).

Mab (Follower of the Endless, from Sandman) either fish, dogs, ravens, or rats as appropriate as based on which aspect she was in at the time. Some times she had the Lil' variant of the relevant Endless.

Artemis (Follower of her namesake as the Dark Goddess) hounds.

Merlyn (Hermetic) Lego Death Knights (swarms at force 9...) or South Park Characters.

'Half Magic' is right! Sad thing is that I woke up in the middle of the night yelling that phrase.

Ja, four levels of initiation and a power focus means you can get pretty intellegent watchers. As he used summoning materials for a year he had to take the drain as the TN was in the thousands. He had the asprin ready for that light stun.
There is only two sensible reasons for having a watcher last this long and at this power.

The first is to show your magical might, which he needs to do as he is lecturing but a troll mage.

Second is that he is expermenting with watchers in a manner that no else has tried. It's exspensive but ground breaking in theortical conjuration for the academic community.

Others watcer spirits I have had.

Blazing comets.
Large termites (bug shamen)
little Fremin warriors
Owls
Bats/ hounds (vampire psychic)
Eagles
willo the wisps like orbs.
fae imps
librarains (chaos mage/UMT)
characatured cats (chaos mage/UMT)

You know, lotsa people don't bother about their friends in the vegetable kingdom.
They think: What can I say?
What can a person such as myself say unto a vegetable?

In SR4 they have the potential of doing a 1 pt attack IIRC. Which seems pretty pointless until you run into a room stuffed full of them. . .

Rofl. That would be great.

GM: There are watcher spirits in the room.

Player: Ok, I ignore them.

GM: They start to attack you. Roll body.

Player: I think I'll be ok...

GM: Roll body 40 times....

Once again we were saved by mana static....