The last sign was intended to represent "Don't get any bright ideas" which would make Derek's guess the closest. And that figures since he's known me the longest. Let's see if he gets this one:
Just remember, this isn't really a contest. Just because you don't think of what I thought of doesn't make you wrong (unless you are Derek). In fact I liked Heather's and Robyn's answers better than mine. So please, take a guess.