It looks like it had a suspension on it at one time so, it probably hung from a ribbon originally. The blank space on the back could have been for an inscription of some kind. These kinds of things could be a souvenir of some kind or a gift for a family member from a crewman. There are tons of similar things from various regiments and military related events in Germany in the 1890's and early 1900's. You don't see the Navy stuff as often.
