I picked this up at an estate sale a couple of years ago, I think I paid a couple of dollars. I tried to find out what unit/boat it came from, and the best I could find was some sort of Motor Transport Boat or Motor Tugboat; basically a harbor type boat that carried equipment or personnel around the port. Never did identify the actual boat or where it was, but I did find out that there were several thousand of these boats (of various types) that worked in and around the port facilities around the world.

It's about 3 inches in diameter and made of Sterling Silver.

If anyone has any more information, feel free to put it up here.

 

Here are the markings on the bottom/back.