Mine is the stock unit, in a purple snap-on protective case, but the back of the unit (underneath the protective case) has my username permanently etched into the back and the etching filled with enamel paint, just in case I lose it or have to prove it's mine.

This stems from when some jerk tried to steal my childhood Game Boy, but was foiled by the fact that I'd written my name on the unit behind the batteries and thereby proved "their" Game Boy was mine.