My best friend is a state trooper here in Colorado. He said, at least in Colorado, as long as I didn't deface or remove the VIN numbers stamped on the frame, and if I told the buyer (
if I were to ever sell it) that the frame had been replaced and modified, there would be no issue. He said the biggest problem would be in defacing or trying to change the VIN on the frame to something else.
I call it the step notch, but "Z" or "S" I suppose would work too