Should private shops have public service style "Abuse of our staff will not be tolerated" signs?

In my opinion they should- back when I was a cashier the amount of abuse I got- man this one guy I still clearly remember- I wanted to grab his head, smash it onto the counter and watch his teeth go everywhere!

"But they're having a bad day"- my now wife was in the hospital for an emergency appointment for her blood pressure and considering she had a ruptured aneurysm I was terrified- but that day guess what- I still treated all cashiers like normal himan beings!

Please don't think I'm here to berate you if you disagree, all comments are welcome- I'm not a snowflake who melts down when someone disagrees!