For a militaria display like that, how about a musket over a drum draped with flags.
Maybe kind of generic, but instant reqognition value and association are high/max for the same exact reason.
EDIT - Or maybe something like the below logo - obviously with significant enough changes and your display on the banners, so as not to infringe on somebody elses logo.
With both suggestions, the general idea is to invoke images of what the public is about to see/experience in the display i.e. in this case militaria.