I love Hyatt’s notes on Recovering the Lost Art of Note-Taking. I like the symbols he says to use:

Use symbols so you can quickly scan your notes later. I indent my notes from the left edge of the paper about half an inch. This allows me to put my symbols in the left margin. I use four:

1. If an item is particularly important or insightful, I put a star next to it.

2. If an item requires further research or resolution, I put a question mark next to it.

3. If an item requires follow-up, I put a ballot box (open square) next to it. When the item is completed, I check it off.

4. If I have assigned a follow-up item to someone, I put an open circle next to it (similar to the ballot box but a circle rather than a square). In the notes, I indicate who is responsible. When the item is completed, I check it off.