Probably this is one of those stupid „teaser“ ad campaigns... It should make you wonder for days untill you see the final billboard. 

So, in your case it has reached its goal ;-)

My way of coping with this stuff - when I see a stupid billboad I say to myself one of the following:
„Not again.“
„OK. Whatever“
„I am not getting excited or curious“. And I don't

Anyway, good observation.