Denny's used to do a pretty good breakfast but the last time I ate at one everyone in our party got food poisoning (including my Mother-in-law). Never again.
I'd ask for the manager on the way out and let him know that you will not be able to come back with that sign there. It's a shame you are giving them money today, but you are already into the meal with your family. Do you need any no guns = no money cards? I frequent Dennys, but not that particular one and would be quite put out if I saw that sign at one that I went to regularly.
Here is a free sample for you to print out
https://www.indianagunowners.com/forums/carry-issues-self-defense/160720-no-gun-no-$-cards.html
Good point. As stated earlier, their food could also be considered a WMD.No weapons? Don't they have silverware?