STV51

I have asked this question before - but you never know! I have an early bushing STV51 which is stamped Chromed on one lug and AAA on the other. I wondered if this had been added by someone but I have just seen a similar 56 version on ebay with the same markings. anyone know the significance of the AAA marking?
Thanks,

I have one here. Brand new bare case. AAA Chrome. Looks like factory markings. I've also had several go in and out of my stores. Email Frank Bowman. He will know. ([email protected]).