This is my male beardie, Hydra! In this image, he's asking to go outside. He does this by putting him arms on the rim and sometimes scratching. He's learned that if he wants to go outside or explore, this is what he needs to do. What bevahiors have your beardies learned?
They are quite clever and learn by routine and repetition. It's good that you've been able to establish some communication with him that way. You can teach them to poop outside of their tank using routine as well. Just put them in an easy to clean area at around the same time daily and they will learn that's the spot to go. Warm baths can help with this training (in the same area) if they like baths (not all of them do).