I used a Testors pen. Easy as pie, but it wears off fast. I'd rather not do it permanent, so I don't mind that so much. It's a relaxing thing to do on a rainy night.

Looking at the pinstriping on my old Raleighs, the barrier to entry is pretty darn low. Some of them are awful sloppy.

Putting the frame in a bike stand, where you can rotate it all around and lean on it while you do it makes it way easier. First time I did it while the bike was just sitting there - it was kinda comical.

Sorry, I only have crappy pics: