World Lock
From Growtopia
Locks the whole world, your name becomes green, names of the allowed players become greenish.
The world lock costs 4000 coins and is currently the most expensive item in the game (besides Signal Jammer, which is the same amount). No one is allowed to break things in this world besides the owner or players allowed in the configuration screen.
World locks are barely ever used in trading, but if they are they should demand a very high price.