This move is known by at least two names, the pencil hold and the iguana mount. No idea the origins.
This is one that you must carefully listen to your body. This move isn't for people with weak or injured shoulders. When everything is fine you should not feel anything in your shoulders at all. The hardest part will be moving up or down. Once your are actually upside down in pencil you really feel quite secure which is unexpected but you'll get used to it.
This is a shoulder heavy move so if it's at all painful stop immediately. Pain that lasts longer than 3 days is likely and issue. Prevent that during training by learning to recognize when a move hurts because it's new or because it's not right for you at this time.
The comments section is always open. Feel free to drop a line, ask for a specific move if I can do it I'll shoot the tutorial if I haven't already.