Hello Mike and Welcome. The short answer is that a merchant would come to the mint and purchase ... for the office of assayer, and the assayer put their initials or name on the coins as they were treated as commodities. The importance of these coins in the Colonies cannot be overstated. It is a well documented interesting subject with tons of information that cannot be covered here. So without being long winded it is most likely the name of the Assayer or his agent. I hope this helps.