Did you inquire within as to the nature of the sign before jumping to the foregone conclusion they were anti-gun? Now this commentary is riding the thin edge, for me, but I had to ask. I tend to conclude, as did you, right, wrong, or indifferent, that a sign of this type is not an invitation but a warning that they are not friendly to gun owners...and you would be 100% correct in calling them hypocrites if that turns out to be the case.
One the other hand, perhaps a lot of gun friendly types keep showing up at their shop with their guns, some loaded you can be sure, looking for a fit-up to their lasers and it is scaring the help/owners. In this case, the sign could be adjusted for a more gun-friendly warning.
Let us know.