I believe that bugs prefer the tight, dark, places, one of which is the rear of the mount against the wall. I arrange to have a surface below, against the wall- a bookcase or a shelf, or even a small strip of wood with no other purpose, so that I can easily see fallen frass and take quick action.
Sign or no, when I go off on a hunting trip I leave behind my wife and instructions to bug-bomb the room that contains my mounts.
(I keep my antlers brown by being a smoker. Everything else turns a yellowish-brown, too, but I suppose that's a small price to pay.
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