Who needs punctuation?

I spent my time waiting in the security line at JFK trying to decide if this banner actually needs a question mark.

It wasn't really a problem until I started repeatedly reading it out loud with different inflections.
There's an old rule of thumb that says you should never phrase a headline as a question, because people may not think of the answer you want them to.
I say go ahead if you have a good reason, but at least use the proper punctuation so we both don’t look like idiots.