Great point you bring up, schmitty. I had NEVER even thought of this issue.
Based on your post, I'm thinking of printing out a sheet of steps and putting it in the vehicle, using this as my translator:
http://world.altavista.com/
I haven't given it much thought, but something like "empuje el boton dos veces para encender el motor" (push the button twice to start the engine) or something.
Anyway, I'm sure with all of the brains we have on this forum, we can come up with something that works.
Oh, just thought of another'n : "No dañe mi coche, o usted pagará infierno" - Don't damage my car, or you'll have hell to pay. :-)