The short version is subscribers and support team members can choose from available avatars, one of the perks of supporting this site. So I guess you could say rethnal was right in a sense. The custom avatars are obtained by being nominated for contributions to the site or your fellow DRNers in some manner, by helpful posts or maybe going out of your way to be helpful at Dirtweek. These aren't the only ways mind you, just examples that I know of. Someone else with better writing skills and more info may chime in here soon....
Hope this clears some of you confusion for you.
Randy