Not in Des Moines
The 2 BW3's in Des Moines do not post these signs. The Dahl's grocery store I've gone to for 20 yrs and that my son worked at before he became a local news anchor posted one in the past year.
I don't think the DSM Buccaneers hockey rink has such signs, but Sec Taylor Stadium, home of the Iowa Cubs, might.
Very oddly, the Martin Marietta limestone shaft mine in Ames has a sign saying "No Knives". We get our limestone there for ready mix. I do not pack at work.
I just ignore such signs. My S&W 638 is nearly invisible and something as big as my .45 is cumbersome and just invites trouble.
I'm told in Iowa, the sign means nothing. They must tell you verbally you're not welcome.