Do any of the types of spirits have any links, or a signature that might be used to find the original summoner. I thought there was something like this, somewhere. But well maybe I'm looking in the wrong part of the wrong section, or perhaps I'm not reading it, and should be because I'm only skimming.

A mage/shaman will know if any of his spirits is destroyed, or an Astral Barrier he built is attacked, so there must be some kind of link. Another different question is if that link can be traced.

Since they are created by a use of a Magical Skill, all summoned spirits bear the astral signature of their summoner.

I concur with Necrotic Monkey here: all bound spirits bear the astral signiature of their summoner. However, whether spirit powers themselves leave behind the summoner's astral signiature is less clear. I suggest that they do, but do not know of any canon reference to specifically back that up.

Since the spirit leaves their own astral signature behind, and that signature is tainted with that of their master, use of their powers will also leave their signature behind. Tracking with it will likely lead to the spirit, but from there you could go directly to the magician. Anyone who sees the signature (ie, gets three suggests on his Astral Perception Test) will also recognize it as the work of the magician, too.

I'm of the opinion that a Spirit leaves its own astral signature behind when it casts a spell, and no signature is left behind of the summoner of that spirit. I'd love to see a page reference if anyone thinks the rules say otherwise.

I would say that ritual tracking can lead one to the summoner if the spirit is bound, and sympathic magic could do so even if the spirit were free.

I recall no rules that allow one to track anything based on the Astral Signature left behind. However, one can track the link from active spells and foci in the same way as spirits. Those links may also be hidden on a Metaplane per MitS.