You can use a Signet of Ressurection more than once - but only if you kill a boss. Killing a Boss monster will recharge the Res. Signet - or it used to do so.. I hope that hasn't changed (or I'll look really silly! hehhe.
Note - A Boss monster will have a colored auro around it. This way you can tell a boss monster from a normal monster as well as what profession it is.
Red = Elementalist
Light Green = Ranger
Dark Green = Necromancer
Blue = Monk
Purple = Mesmer
Yellow = Warrior
Of course in Pre-searing the number of bosses you'll run into is fairly limited.. so don't expect to have it recharged all that often
1. The Academy is a place you'll go to once you have your 2nd profession and talk to Sir Tydus. He will send you to the Academy for some "training". This trainign will be a very simple 4 v 4 PvP - that is you and 3 other's on your team will fight against 4 others on another team.
Note that since you can only have 2 people in a group, there will only be 2 players on your team and 2 players on the opposition team. The rest of the spots will be filled up by AI Henchmen NPC's.
Also note that once you accept the quest from Sir Tydus you can
NEVER go back to where you were before. It's a final moment in that part of the game - note the red warning in the quest text that you get when you talk to Sir Tydus. So make sure you have completed everything you want before accepting the quest from him.
2. The Academy is located behind Armin Saberlin and Sir Tydus - note the big gates behind them.. that blocks the bridge which leads to the academy.