Agree on both counts. Post strike damage and circulation wear to the coins. The quarter MM, yes you may want to have someone take an in hand look to see what's going on there but I am thinking die deterioration. Just guessing on the last part.
Quite probable that it is initials. It would be interesting to contact that lodge and find out if in their records a person was a member that year with those initials.
The mark you see in the center of the keystone should be the mark or identifier of the origional person that was given the coin in lodge. This would have been added by that person to the coin.