Cvar:
sm_formatted_hostname "My Server %d/%d" where first %d - current count of players, second %d - value of sv_visiblemaxplayers Version 1.2:
sm_formatted_hostname "My Server %d/%d (%s)" where last %s - server version (plugin gets it from PatchVersion in steam.inf), very useful for L4D2 server that is updated every week