Stolen from Holycoast.com

Here's a thought.  Most of us with computers also have some form of printer.  Get yourself some Avery Labels (the 30 to a page mailing labels are about the right size) and simply print out a page full of them that look like this:

That's all you need to say. The sticker is small enough that you should be able to stick it on the pump near the purchase amount and it won't be terribly obvious to someone watching. However, everyone that uses that pump will see it and be reminded why they're paying the ridiculous prices they're paying.

"Memento mori"
(Me)