It's on the inside of one of the straps - that's where the crafsman recommended it was put. I got to see it being done - fascinating!! We were lucky to have a craftsman visit the store last year, and I had it done then...it was free of charge. They do it in the colour to match the bag. ie: My Kelly has a silver stamp, so the monogramming was done in silver-leaf. They have gold, silver, marron fonce, rouge H, noir...can't remember the rest.
One of my bags is just heat-stamped with no colour, but has gold hardware, and when I asked about that one, they said they would heat-stamp the monogram, if I ever decide to have that one done.