Who said not tell anyone about it?

how about this,

HAPPY HOLLOWEEN! many activities have been added for the new season!
get ready for some spooky thrills and exciting challenges!

tada... people now know there is an event and they can go explore and find whats added and if there are more hidden events you can add special items... wow the game got so much more exciting.. people exploring, and teaming up to look for interesting new things.

your right sounds WAY more fun