I like the idea of sending their trash back to them.
My wife was just saying the other day, we don't see the road side signs that say "no littering and x amount of $ fine", any more. They may be there but we just haven't noticed them. I can say in general that littering has gotten out of control in our area, (just north of Sacramento) It is ridiculous the amount of road side trash and actual junk, from chip bags to mattresses and sofas. I remember years ago there was many programs about littering, from whole litter bug thing to the American Indian sitting on his horse shedding a tear.
Adam, thanks for bringing up the topic of littering.