I use a pen, essentially like Don but a little more modern
A regular ball point pen works in most instances, but if the wood is overly wet it doesn't always do too hot, though you may be surprised.
A higher quality ball point seems to work even on wood that has just been rained on, at least that is my experience.
I don't like to use an awl, because sometimes it gets caught and follows the grain when marking parallel to it. Knife lines are nice in instances that require supreme accuracy, which in general when working in green or somewhat green wood, such accuracy is an exercise in futility...
