Public Display of Affection on Public Transportation

I've never been a fan of PDA on either side, both the watching other people make out or myself making out with someone in public. Then I saw this picture. I'm not sure how I'd react. What do you think of public displays of affection? Would you say or do anything about this?

Me, truthfully, I probably wouldn't have even noticed because anytime I'm anywhere trying to mind my own business I'm nose deep in my iPhone, but something like this picture would be hard to miss. Some lady on top of some other dude who's on a wheel chair. I'm also hoping they actually knew each other before this picture was taken. I'm guessing he didn't board this shuttle and some girl thought to herself, "Oh, he's already pinned down, he'll be my next victim." Weirder things have happened, I suppose.