That was the case in a former building I worked in. After sandy hook the building owner was asked if he was guaranteeing our safety by posting a “no guns permitted” sign. The sign came down the next day.
Send that question to places like Half Price Books.
After the open carry passed in Texas, they put up signs saying ‘no open or concealed carry’ & cited the 30.06 and 30.07 sections of the state code.