Okay, so we're all agreed that one use of the apostrophe is to mark contractions - spaces in words where letters have been left out.
So what are we supposed to make of this apostrophe, spotted during a petrol stop at Asda, Cardiff Gate?
It definitely says Drive Thru'.
Er, Drive Thru-what?
Drive Thrush? Drive Thrum? Drive Thruppence?
Drive Thrumwort, Drive Thrutch, Drive Thrum-eyed?
Drive Thrust, perhaps.
Read as an imperative, it might stand for 'Drive Thrummingly', a sensible exhortation for us all to drive in a monotonous manner (the apostrophe being necessary because 'thrummingly' would never fit into that small space).
However, I suspect not.
I would like to meet the person who thought this apostrophe was a good idea, and shake him by the throat.
I'm with the panda on this.
PS It definitely wasn't bird shit.