what is a sanction

[dev1428] Sanctions can now be received from all three Grand Companies, regardless of affiliation.
To receive sanction from a Grand Company outside their affiliation, players must first have completed one of the Don't Hate the Messenger quests and have been promoted to at least sergeant.

what does that mean? can we do multiple GC now?

It's extra stats on weapons/gear you get from your Grand Company. You lose it when you die, so now you can refill it at all Grand Companies, not just the one you are from.

Sanction = awesome stats on some GC gear

ok i was hoping for the ability to do multiple gcs