Chris, I notice the very same markings on mine just recently when I glass Beaded them. I could not see it prior to blasting cause of the corrosion and peeling paint. I looked for a photo prior to paint and could not find one, I recall it was very faint. They were shallow and crisp just not very deep. I think others here might know the supplier it "stands" (Identifies) for (?). I just checked the parts bag and the stamps are on the outboard side, low towards the mounting hoels, and very very faint, the primer and orange has basically filled it in. (GT)
JIM