To @Tony B
: Sorry to disappoint, but I am working it off as quickly as is reasonable. I don't have a huge supply, just a wide-ranging collection of small pieces, many from the priced-per-pound bin of cutoffs at the woodworking store, or donations from woodworkers at my local club. I want to remember the species for later. Sometimes I get a piece of wood from someone, and want to make it into something for them after it is thoroughly dried, and I want to remember who it is for. What else can I say?
To everyone else:
Thanks for the helpful input from everyone. I am still looking for a good way to label wood. Easy to read, durable, easy to remove years later.
Pencil: Doesn't show up well on dark woods. I tried colored pencils. They are waxy, were not easy to read, and did not remove easily.
Lumber Crayon: Thanks for the tip. I had never heard of them before. They looked promising until I found articles and info suggesting that they are hard to remove, and advice not to put marks in places that might be visible later. Okay for construction lumber that is hidden in walls, etc.
I think that maybe handwritten paper strips held down with Scotch Magic Tape (yeah, office tape) might be the next thing to try. They would be hard to peel off after years, but I bet they sand off easily enough. I assume that the adhesive won't damage the wood below the surface.
-> I hope other people have found better answers and will share them here.