Again that depends on your state. In some states no gun signs have the force of law, and its illegal to ignore them. In some states they don't, and its just a bad idea. Ask a local lawyer if you need to be sure, or check your state laws yourself on the internet.
And sometimes they're legally required but have limited applications... For example in MY state, that may not be the same as YOUR state, it's illegal to carry in a bar, but you can in a restaurant that has a bar section AS LONG AS you don't enter the bar section itself. The bowling alley I bowl at has a restaurant and bar. I can legally bowl, and eat food in the restaurant, but I cannot walk into the bar section to check the score of the game on the big screen. However, all of these restaurants are required to post a no-firearms placard. Most do so on the front door, rather than on the bar door.
And for the record, I don't carry while bowling- I hit my leg with the ball from time to time as it is, and don't need to hit the ball on my pistol.