I agree. They're just posting something that didn't change any law or permission. Patrons could have carried guns inside already. Virtue signaling to a different crowd.
In reality, this is more of a sign to ward off a certain demographic, rather than welcome a certain one.
Also, depending on the area, it may not hurt to advertise the fact that the clientele and possibly the employees are armed.
This is also the result of continued attacks against gun owners and the second amendment. At some point, staying neutral when there are people actively seeking to harm you or ruin your way of life is a really bad idea. This is an obvious and inevitable reaction in the face of repeated attempts to smear gun owners and steal their rights as American citizens.
The owner said the sign's been there for years and no one noticed or cared. He hired someone to do a social media page and they put it on it - LOL - I'd fire the idiots for stirring the pot on a nothing burger. But he also say's it'll stay, (paraphrasing) because he has been robbed frequently and wants all to know he and people who go there aren't afraid to defend themselves.
Bad idea to mix your business with any sort of political controversy since it alienates customers.