Are you a pin collector? Then this forum post is for you, because I’m going to tell you the rules we follow when club penguin have hiden pins!
Rule 1: If club penguin have hidden a pin in a room, they won’t hide another pin in that room for at least two months. So, for instance, the Anchor is hidden in the Cove, so they won’t hide another pin there until at least May.
Rule 2: club penguin won’t hide a pin in the Town Center. That room is the busiest room in Club Penguin.
Rule 3: club penguin won’t hide a pin in the HQ. Not all penguins are agents, so they wouldn’t get to go there.
Rule 4: A pin won’t be hidden on Rockhopper’s Ship. Rockhopper doesn’t usually stay for two weeks, and the penguins don’t want him to leave with the pin!
Rule 5: club penguin try not to hide a pin in the same place twice. The next time a pin comes to the Cove, club penguin are not going to hide it on the log by the bonfire.
Rule 6: Pins usually look like something related to a recent update. The Anchor was related to Rockhopper's ship, and the next pin... hmm, should I give you a hint about what the next pin will be? Sure, why not?

Pins are pretty small, so it's hard to give a hint without giving it away!
J3CP - Edited from the club penguin blog