I love this one.

I'm easily amused but another unintentionally funny one I saw was a sign, on the ver top of a lamp post,saying ''retirement home for the elderly'' with an arrow pointing to the heavens.
Finally this wasn't a sign, but when I was in the Dominican Repbulic when you borrowed a towel from the hotel, you received a piece of paper saying amongst many things, 'please rectum the towel before 8 pm on the day of rental'
We presumed, and hoped that they meant return.