Function ShowPlayerNameTagForPlayer toggle the drawing of player nametags, healthbars and armor bars which display above their head. For use of a similar function like this on a global level, ShowNameTags function.
ShowNameTags must be set to 1 to be able to show name tags with ShowPlayerNameTagForPlayer, that means that in order to be effective you need to ShowPlayerNameTagForPlayer(forplayerid, playerid, 0) ahead of time(OnPlayerStreamIn is a good spot).

(playerid, showplayerid, show)
int playerid Player who will see the results of this function.
int showplayerid Player whose name tag will be shown or hidden.
bool show 1 - show name tag, 0 - hide name tag.

Return Values:
  • 1: The function was executed successfully.
  • 0: The function failed to execute. This means the player specified does not exist.

//The player who typed /nameoff will not be able to see any other players nametag.
if (strcmp("/nameoff", cmdtext, true) == 0)
    for(new i = GetPlayerPoolSize(); i != -1; --i) ShowPlayerNameTagForPlayer(playerid, i, false);
    GameTextForPlayer(playerid, "~W~Nametags ~R~off", 5000, 5);
    return 1;

Related Functions
The following functions may be useful, as they are related to this function in one way or another.