Framebuilders - Serial numbers

Simple. How would one go about putting a serial number on a bike? Metal stamps? Where you take a hammer and tap the number into the metal? Or something more complicated?
I've been curious about this. And since I'm planning on building my first frame soon (hopefully followed by many more) I wanted to know.
Thanks
-Gene-

bottom of the bottom bracket shell is the usual place.

I know that.
How? Is it metal punch engraving? Dremel it in? Do you heat it before you do it?
That's what I'm curious about.
-Gene-

http://www.harborfreight.com/hand-tools/stamping.html

http://ajh-knives.com/supplier-2.html

These are sharp, properly spaced, and durable (and expensive, though good value). Many of the "sets" have rounded letters, and numbers that do not make a crisp mark, and they space rather far apart, and getting them perfectly in line can be trying.

Or maybe this:

http://www.britishblades.com/forums/showthread.php?41757-Simple-blade-etching

Lots of youtube also.

Number set like Scooper linked to, applied to the BB (non-drive side) with a ball-peen hammer, going with the radius of the shell (i.e. the letters are on the same line as the edge of the BB shell).

Of course, for the number "1", you could just use a file.