I used to be trapped with the fairly mortifying moniker "CoolCars42" on 360, because I wasn't one to choose the name.
When I got my PS3, I elected the name "SteelVines". Unfortunately, I had to replace the first to e's with 3 so it became "St33lVines". The reason behind this I think derived from fiction that I planned to write, one which involved metal vines over growing the world. I can't remember the concept precisely. It may have also been inspired by another work of fiction I was going to write but unfortunately failed, which involved blood being turned into metal inside the veins as a symptom of a disease.
I later created a new account called SteelSolo. This is my current PS4 account. It's a sort of portmanteau of my original moniker and the fact that I play Rocksmith a lot, hence the Solo part.