I've just seen that all spells (beside Combat) have a "Restricted" legality. What does it means?
How can a mage PG pass a "legality" check (maybe during a perquisition or similar)?

If the mage uses a spell in public, and they aren't registered as an authorized practicioner of magic (i.e. are licensed), then they could be in trouble.

At least that's my reading of it. Also, spell forumla and such would be restricted/forbidden.

Any awakened character needs to be registered as such in his SIN, in most countries. Buying spell formulas is of course restricted to registered mages.
In RAW, that means having a (fake) licence.

The legality refers to the formula itself. Spells can't be restricted as they are an expression of Nature.

Ok, but if you (a shadowrunner mage) want to buy a formula "legally" you need a "good" fake SIN stating that you are a mage, right?

If you find yourself flinging Stun Balls around the city without a licence though, count on KE to stun your balls and drag you to court for either registering or criminally deviant behaviour if you're a SINner, or being thrown in with Bubba and a cyberzombie otherwise.

Knowledge of spells might not be researched, but use of them certainly is, and restricted too.

Or have a black market contact.

Or design it yourself...

And subsequently buy it from yourself?

What a bargain, and you make impressive income to boot, by creating it for 1/2 price and then selling it yourself for Full Price... Sign me up...

Wait.... *confused* Um.... That works, right?

In previous editions, anything Force 3 or higher required a license. (Any force Combat spell required a license as well) In 4th Edition, it looks like they simply made it so all spells and foci require a license. Since KE and LS can't run around mind-probing everyone to see if they have knowledge of magical formulae, I take it to mean that anyone who casts a spell in view of the public, or leaves a signature, can be investigated for a license and possibly brought up on charges (if they lack the proper licenses).