I think a licence plate you could get custom would be pdffile.
We once had a buddies aerostar that screamed creeper. We took painters tape and wrote free candy on the side, then in the back the fine print of "we're legit".
I think a bumper sticker that said something like "pedophiles don't drive pedophile vans." or "If you're close enough to read this, and under the age of 14, would you like some candy?"
And maybe a bucket of gummy worms on the dash for good measure.

