Not sure what this accomplishes...just thought it might be appreciated...

I've seen that more than once, especially on old English bell strike GF's. The one I used to have was loud! My wife called it our trolley car.

Neat trick, I'll have to remember that one! Looks like an attempt to 'soften' the clang when the hammer hits the bell.
Just had another thought, could it be preventing a grub screw or locating pin for the hammer head falling out?
Best regards
John

My hammer was cast one piece with the shaft, so no grub screw. Don't now about Greg's.

No this was also cast or attached in some other way at least.

I'm not sure why it would soften the sound of the bell as it is on the opposite side of the hammer. The case is too large for the back of the hammer to hit anything.

There was also a piece of Electrical Tape wrapped around the post that the hammer is attached to(this scared me). The reason I found out, is that when the clock struck...the post that the hammer is attached to hit the plate post of the movement.

Greg, perhaps not only was the hammer plastered-the clock repairer might have been also!
Mike C.