I've been known to use an ancient Dymo label printer, the kind that embosses plastic strips. In most cases they last forever (on some surfaces they won't stick though). For large panels you'd need one of the better models though, labeling 40 circuits with a Dymo Omega sounds like a major pain in the rear (the last panel I did had a whopping total of 6 circuits, if you have a 230V 2w single phase service any more than that seems pretty useless).
