The only way to tell is if if they have the same name on the forums as on in game...like my self b/c it will say they are a Server admin or Jr admin or something like mine does. best way to find out if they are admin is to send them an admin message... i think its done by doing a Teamchat With the @ then sapce then mg..so...."TEAMCHAT@ MSG" my button for teamchat is Y. so for me it would be "Y@ MSG"

otherthan that if you think that someone is impersonating an admin...i guess you could post there name and steamID on the forums by tpying status in your console an then copying then name and STEAMID.