Sure Signs of Boredom:

Your toothpick model of the Eiffel Tower is approaching life size.
You actually start doing things on your 'to do' list.
You invite Jehovah's Witnesses in for a chat.
You start reading the dictionary to learn new words.
You wear out your computer mouse playing solitaire.
You start taking things apart just to see if you can rebuild them again.
You master the art of sleeping with your eyes open.