It seems like several businesses have posted pro-gun signs. Is there any reason to (or not to) make some sort of standard pro gun sign and ask places to put them up?

It seems obnoxious to me. If someone wants to run an inherently apolitical business and they don't care one way or the other if their patrons are for or against guns, I see no reason to pressure them to risk limiting their customer base by offending some sheeple.

If they want to do it on their own, kudos to them. If you want to be a provider of signs to these folks, kudos to you.

I agree with ree.

And in case anybody does want one, here's one I made, which anybody's free to use. It's vector art so it can be printed at any size in high quality. Also I'd be happy to customize one with a business name and custom art for a very nominal consideration: