When I first started playing WC1, I didn't fully understand what a "Callsign" was (being only, like, six years old at the time), but I figured it must be some sort of military word for "first name," because that's what everyone always called me in the game. Later on, though, I wanted something that sounded threatening, fast, and aggressive--which, ironically, was typically the complete opposite of my play style--and I picked "Rampage," which sticks with me to this day.
The "3057" was added a little later as a Battletech reference once I discovered Mechwarrior 2, and since the internet was just starting up it wasn't uncommon to see "Joe51" or "Killer682" or the like online, so I kept it as my own personalized number. I've been thinking about retiring that nick and moving on to something else, but it seems to have stuck...