(Mori)Bus Philosophorum: Seriously, What the Heck is That?

(Pardon me for the poor camera phone photography.  It's kind of tough to discreetly snap a pic on a full, moving bus.)

This is something that has perplexed me for a while, now.  What the heck is that odd shape next to the man's head in the upper right corner of this inspirational CDTA poster?  For the first few weeks I wasn't looking at it analytically, and my brain interpreted it as a graduation cap but...it really isn't.

Here's a closer look. 

Is it a tie?  A thought?  The leg of a giant wasp?  (In which case, look out, Racially Ambiguous CDTA rider!) After months of wondering, the best I can come up with is that it was just a printing mistake, which is obviously a boring conclusion, so I'm going to hope (imagine) that the real explanation is better than that.