Lightbulb

You are thinking of something to build, Then you come up with the idea, Let's make a picture of us building a picture of us!

You just erased your entire city save, Then you come up with the idea, Let's ask the server admins if they have a recent save.

Both of these can be described in comical use by a lightbulb appearing above their heads, Not just ideas though, you can use it in other ways, such as, questioning:

I have an idea! Let's think of a way to fix this

Or disrespectfully

I have an idea! How about you get out

Or philosophicly

I have an idea, Or do I, Or is the proposition of having an idea invalid all in all?

You can use any of these, Simply download this file and type /idea in game.