What is the story with the AS seat clamp bolt with raised letters

[Dave K]

I picked up a post war DX today (serial number B50632) that had this seat clamp bolt with raised letters. Were these only used in 1946? The bike does not have a tapered kickstand so I would of assume it is a least a 1947 or later. Some one might have added the clamp to it at some point in its life because it has a prewar crank and a wheel set so someone has been monkeying with it in the past.

Thanks for any info

Dave