Shamrock towed me once while I was delivering a pizza, car was left running, with a pizza delivery sign/ad on the roof.

Can't you do something, like, get some rope, and tie off the lot with lots of "no parking" signs, so NOBODY parks there? Who would know who did it? (I am not familiar with this lot at all, I live in IN). Cut off their ripoff profit, and help some poor slob who might make the same mistake. If they won't mark it clearly, do it for them!