It's not SWC Team members, and it's not possible now. It's from the old rules/way of hosting images, where you were permitted to have your SWC avatar link to an offsite hosting of the image. Syn and others use an image rotating script or something like that to rotate their images on their hosted server.
It's still possible to rotate your signature that way, since the Signature is a user-editable html-enabled field.
You'll also notice some people with GIF's as their Avatars, which is also a grandfathering of old rules that are no longer possible.
Similarly, some characters have a single name, which again, is old rules where you were permitted to only have 1 name. It's not possible now.