Tip Jars for Fast Food?

In a fit of fast food weakness, I stopped by KFC while out at lunch on my bike. I wanted to try one of the Buffalo Snackers (short review, not especially good, it has a funky flavor that's pretending to be real spices or something).

Anyway, at the cash register they had a big jar with TIPS prominently written across the front.

Who tips at fast food? Apparently someone did because there were a few bucks in there. I'm pretty sure the higher ups at KFCHQ would not approve.

And no, I did not pony up $.15 for my dollar snacker. While I appreciate that fast food workers are underpaid, overworked and underappreciated, tipping generally involves some level of service beyond getting a sandwich and putting it in a bag.