It seems to me that it would be most ethical to do so. It might also avoid the problems an inaccurate report would pose. IMO, a polite notice that their business is about to receive or has received some unfavorable publicity would make it harder for a business to object or accuse you of slander, etc.
I would accompany such notice with real-world statistics like the number of gun-related incidents of any kind that have been prevented by a 30.06 or a 30.07 sign (zero!) and the number of licensed gun carriers who will avoid their establishment (you would have the numbers on this). Doing so might not convince the business owner to reverse course on posting these signs but you never know.
Finally, you should also offer to publish any future notices of the removal of the 30.06 or 30.07 sign (if they eventually see the light
)