I too got some Ideas.
I have think of 2 stuffs.
1. You guys have to write Post4VPS or something similar ingame, by shooting them on stone,ground or by placing cars/vehicles to form such words,etc
here are some example:
and the winner would be excluded from monthly post count of January.
2. Signature competition where users would first participate by posting in the thread where this contest would be held and after that I would take random users from the participated users and assign them to make a signature for other random participant, and in this way all participants would get an username for whom they have to make a signature image containing user's username in that (the size should be somewhat like a banner).
Like 4 users have participated - test, demon, dummy and bot. Then I would randomly say test to make a signature for an username called dummy, similarly I would tell dummy to make a signature for username called demon, and lastly I would tell demon to create a signature for username called test. And assign a date at which all participants would be getting surprises from other participants
but guys keep in mind, in this process participants should not reveal what username they have got otherwise it won't be a surprise.