It's common knowledge that any game produced for the Mega Drive / Genesis after July of 1992 will most likely be region-locked, due to the introduction of the TMSS chip.
What I'm interested in, though, is the original model of the console, the one that came with Altered Beast as a pack-in. It had no region lock of any kind - is there any way to distinguish this model from the zillions of others without actually trying a game? i.e. are there any distinguishing marks or features on the console itself?