go for the classic 70's licencse plate frame:

"gas, grass, ass ... nobody rides for free!"

or, maybe,..

"if this benz be rockin',
don't come a knockin!"

you will radiate class and good taste.

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"The law, in its majestic equality, forbids the rich as well as the poor to sleep under bridges, to beg in the streets, and to steal bread."