There is another way and some knifemakers use a hardened steel stamp and mark the blade when it's in its annealed state. The stamp will have to be machined/engraved and hardened and will generally have limited detail vs. a stencil.
For me (and lots of other knifemakers), the stencil idea is perfect. A good stencil and a relatively simple AC/DC low voltage power supply works good to make nice black marks in steel.
Attaching the leads from the etching power supply we must always put the positive on the blade. The negative lead will be pad. I soak the pad with electrolytic etching solution (Google that for more info) and start the etching.
Every knifemaker has his/her own schedule, but I for the ETCH phase, I like to do 10 seconds ON (pressing the pad down) followed by 5 seconds OFF (lifting the pad off the stencil). This allows the stencil to cool a little, which increases the life of the stencil. I repeat this etch for 5 times on stainless steel.
After 5 etching cycles, I change the power supply to MARK. In the mark mode, I do 4 cycle of the same. 10 seconds on and 5 off. This seems to produce a good quality mark based on my etching power supply. I would advise everyone to test their method a few times on some scrap steel before committing to etching their first blade. At this stage it's late in the game and a bad etch can mess up lots of hours of work.
I have several sizes of my maker's mark, but I also asked Ernie to make me stencils for all the common steel types that I use such as 154CM, AEB-L, CPM154, CPM S30V and so on.