Help Identify: 1920s Bronze Loyalty badge?

[KevinBeyer]

Can anyone help me with the identity of this badge?  It is bronze, dated between 1925-1929, has the word "LOYALTY" engraved on one of its bars and bears a US Shield and Eagle.  On the pendant, the initials S.M.C. are engraved.  Is it 100% Duty?  National Guard?  A Shooting Badge?  I don't think that it is because normally they include "100% Duty", or "N.G.", or a type of weapon used in the match.  I am stumped.  Standard googling came up with nothing.  Here's hoping one of you has seen one before and knows what it is.

Thanks in advance!

 

Kevin