It certainly appears to be the A/B symbol. A/B has been in business since 1776. It does look old. It almost looks like a piece of collar brass from a uniform but I'm thinking more of Horse bridal ornament. The A/B Clydesdale's are beautiful horses and a must see if you have a chance.
most closely resembles the Anheuser Busch logo in use from 1872 to 1890's, but based on the only thing I could find on the net it isn't exact. History of the A & Eagle | Anheuser-Busch.com