When you want to call a waiter or simply claim the attention of somebody, some foreigners use the top of the index finger above the head moving back and forth.
In Sicily, this is considered extremely rude, because that’s how our parents would call us on something bad we did. I always explain to my guests not to be surprised if somebody does not come to you with a happy face.
Instead, just point your whole index finger up firmly in front of your face, with no movement, and possibly with a big smile…