Often times it's also simply self-chosen. What YOU think you'd like to be called. On my team, we all chose our own "Handle ID's"...
'Reaver' (obviously me lol)
Yeah. Little history lesson about some of us- I was out at a field chatting to some other people and my teammate was calling me. Never heard him calling my real name, which he said several times, including outright yelling. As soon as I heard "reaver" I looked over lmao. "DarkBlade" is a big, burly fella who likes to rock it assault style. 'Raven' is our newbie, a flighty, scrawny bugger who's more of an annoyance to the enemy than a threat. (I named him lmao) 'Flow' is our speedy, CQC guy. He's fast, light on his feet and by god runs like a damn gazelle. As for 'Solitaire'..... He's LITERALLY our Juggernaut. He uses a support weapon to pin you down and flanks you. He's a monster sometimes, at least in engagements with few targets. He's far more reserved when there's many XD
Long story short, it's really what YOU like.