Kinda surprised that no one has mentioned sign language. I feel that it's use cases expand outside the original intent, especially if other people in your circle understand it.
Basically every country has their own sign language or an imported sign language that became standardized.
But learning any sign language will make it a lot easier for you to communicate with signers of any sign language. Not because they’re necessarily similar to each other, but because sign language varies a lot regionally anyway (and even locally depending on what method of signing you’re taught) and it will be much more natural to find ways to work around it and communicate with each other.