Is this an unusual maker mark?

Common on SA daggers. On bayonets not unusual, scarce maybe. This mark is usually seen on short model bayonets with grip plates retained by central spanner nuts as distinguished from Pack's offset spanner nuts.

Billy,

You are right on about the spanner nuts.

Thanks for the info.

All the best ..

MW,

Is there a colored felt tab in the slot?

Yes... Red

OK, not what I had thought. Some of these Aesculap bayonets have been observed with blue felt plugs. The color is interesting as it hasn't been addressed in the references, at least that I've seen. Some have posited that it was for Diplomatic service but there's no proof of this I know of.

Interesting .. I've never seen one with a blue plug.

All the best ..