VAC banned players will have a yellow attention icon in server HLstatsX/GameMe player list and a prominent "Player is banned by VAC for at least one game" on their HLstatsX/GameMe page.

Example:
Name: Ben
STEAM_0:1:2656127
http://steamcommunity.com/profiles/76561197965577983
http://steamcommunity.com/id/B00TS/
HLX:
http://fun-arena.hlstatsx.com/playerinfo/597449
http://tac-rank.gameme.com/playerinfo/59953

Also see:
http://insurgencymod.blogspot.com/2010/10/cheater-ben-steam012656127-wallhack.html
http://insurgencymod.blogspot.com/2010/12/hlstatsxgameme-new-feature-listing.html

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