I like your system, but since I am rather attached to using a small circle for to-do items and a dash for data items, I have used ideas from your system to expand my notational system. Adding symbols for "waiting for" and "delegated" (I put initials before or after, respectively) and noting when something has moved has been quite helpful! I also put a small dot inside the circle if I start but do not finish a task, and box the circle and add a page number if I realize a task should be a project of its own. Thanks for the ideas!