I just find a spot on the back or bottom, write my name or initials and year in pencil, and carve it quickly with the chisels and gouges I have. Don't go for show, just the mark.
Yesterday I used a sharpie marker, not the tiny tip one, but the bigger cone tipped one. I think I like this better than the pencil method. The big line width from the marker showed me where to cut. I use the awl tip of my marking knife to scrape out the lines after I chisel and gouge.
I thought about learning to letter-carve, but it would require I buy $100 or more in carving tools, so I'll just keep doing what I do with what I have.