I used to follow Yale and the writer of Love & Capes (Thom Zahler) back when I was on FB. One of them made mention of some illegal merchandise using pirated artwork (I can't recall which one). He was very appreciative of being informed of it and was able to send out notice to his fans not to buy it.
I'm sure Yale would love to verify if the t-shirt is authentic or not, as nobody likes having their work stolen. Would you like it if DC comics made a movie/comic out of one of your stories without at least crediting you? If it is authentic, then I'm sure he'd love to opportunity to toot his own horn and say "Yes, please buy it!" I've found these artists as friendly as the writers on these boards.
However, I understand if you'd be uncomfortable approaching Dean or Teri to tell them how much you loved them on L&C:TNAoS, then I can understand you being hesitant posting to Yale. Perhaps another reader on the boards can take up the cause for you.
It's a cute t-shirt/picture either way. I'd just hate for someone to have pirated his artwork without him being compensated for it.
Michael