This signal is usually used to say that you are “A-OK” or in some cultures to say that a meal is very good. Most commonly, this signal is used in scuba diving, as “Thumbs-up” means that you want to ascend. But in some cultures such as Brazil, Germany, and a few Mediterranean countries, this signal is used to represent an anus. This would be calling somebody a butt hole. Today not everybody would interpret that gesture as an insult. But if you are going to Germany or Brazil, just saying your ok would be better than making this gesture.