flag gun

noun2

1. •
   A humorous prop gun which unfurls a small flag when its trigger is pulled.

   • "I'm going all out with the props. A rubber fish with a big smile, a bang flag gun, and a kazoo. . . ." — 2008
2. •
   (UK) A gun in an artillery train bearing a flag.

   • Centuries ago the largest gun in an artillery train carried the equivalent of today's Queen's Colour and it was known as the “Colour” or “Flag Gun”. — 2009