Heh. Curious. Not to knock Matthew's suggestions, but do you think it is more important to have a book that others can understand or that you, the SM, can understand? Do you think that if you aim for one you could get the other along the way?
I don't know that communicating entrances/exits to the design team requires the diagrammatic methods SMs use to take down blocking. They can all be handled by standard, text notes and in fact might be more useful in plain text. Do you think that a starting stage manager will be faster taking down the action using some sort of new, uncomfortable shorthand or using regular text? What about when we leave or hand the book down to the next person?
Yes, a picture may be worth 1000 words but what if you're really lousy at drawing? The only reason that I can think of for diagramming, personally, is if you draw faster than you write. I do not.
Personally based on how I think and learn, I need more written words and fewer pictures to be able to recreate a scene. My blocking used a few 1-2 letter abbreviations for character names/SL SR DS US, but almost no diagrams unless I was dealing with massive chorus scenes. It was about 90% text. When I was trying to recreate something in notes for the team it was easier to pick up my own language a 2nd time than try to go back and decipher a diagram, even my own.
If there's one thing I've learned about our shorthand it's that while we have some elements in common with our notation there's other trade secrets and unique glyphs that others might not recognize on a handoff. The few times that I got to peek at other SM's books, I first had to surmount a pretty large learning curve before I could parse their blocking.
Maybe it's just me and my total inability to parse visual input. I don't know.