While removing the front sway bar collars on my 70 W30 I noticed a mark on the collars. It is a M with a circle around it. I searched for information on this mark and found another post with a picture of the same mark, this time on fuel tank straps. The guy that put up the fuel tank strap picture indicated the straps were original to his '70 W30, so I assume I may also have original front sway bar collars?

Does anyone know more specific information regarding this mark?

 

It is most likey a manufacturers identification mark. These are common and particularly useful when there are multiple manufacturers for a single part. If there is a failure resulting in warranty cost, GM would immediately know which supplier to debit.