This is not legal advice nor am I saying I personally ignore said signs, or other CPZs. Just an opinion.
Outside of the federal CPZs, or other special CPZs like restaurants that serve/bars (till the 30th anyway ) it is my understanding if you are caught with your firearm it is a civil matter. My question is if you are concealed carrying, and you're careful, and aware of your surroundings, how would you get caught? Even so, I advise one obey the law to the best of their ability, balancing their care of personal self-defense, with their right to choose the places they do business with.
Also never talk about guns at work. Ever. Unless your work is stated firearms friendly.