The idiots are going to take pot shots at whatever is installed out there where no one is around to witness them. I see two alternatives;
1) take down the sign and leave them nothing to shoot at, or
2) make up a sign on the cheapest chipboard panelling each spring and
figure on it having a short lifespan.
Why spend a lot of money to have a sign marred by gunshots, when a cheapie can be replaced easily? Who knows, the idiots might get tired of aiming at the same target after awhile and leave it alone.