Generally, most clans will have an acronym for their full name, especially in clan tags. (An example would be Plazma Burst Wikia being shortened to PBW.) Clan tags are generally displayed in brackets. Some clans have their own system of ranks, while others have multiple groups, divisions and squadrons within the main clan. Many clans have requirements for their members, such as a decent Kill/Death Ratio or a certain amount Player points.
Most likely, most clans have a decent webpage, chat etc. A lot of clans commonly make alliances and or enemies.