I give them names that relate to the material that I've turned, for the most part they are individual names for each pen, not just each type of pen. For instance, I made a rattlesnake/deer antler segmented cigar that I call a Whitetale Rattlesnake. I make a low priced aluminum arrow shaft and deer antler slim that I call a Bow Hunter. Slims from olive wood are called Genesis 8:11 because that is where the wood was first mentioned in the bible, all other olive woods are called Kings 6:31 because that is another biblical mention.
I also give each pen a inventory number so that I can have several pens named Genesis 8:11, I keep my sales records by the number, not the name or style. Each inventory number record includes the material it was made from, the kit made from including finish, the date made, estimated cost, and asking price.