You need to squirt the stamp book that weird Ed is looking at with disappearing ink.
You can get the disappearing ink early in the game with Bernard (the one with glasses)
From main lobby where you start, go right and up the stairs and to the middle room with R on it, it's on the small table near the door.
Exit from there and go to stairs in to the right. Then go to the door on the right with weird Ed Edison.
Use the ink on the stamp book, Ed will get angry and tell you to get out and then throw the stamp book at you. Pick it up (i also picked up the loose stamp) and then return to Ed and hand him the stamp book. Achievement will pop.