[DanishHaq]

Take a look at these commands:

pawn Код:

CMD:nickoff(playerid, params[])
{
    for(new i = 0; i < MAX_PLAYERS; i ++)
    {
        SetPlayerMarkerForPlayer(playerid, i, 0xFFFFFF00); // the alpha of 00 hides the marker
        ShowPlayerNameTagForPlayer(playerid, i, false);
    }
    return 1;
}

CMD:nickon(playerid, params[])
{
    for(new i = 0; i < MAX_PLAYERS; i ++)
    {
        SetPlayerMarkerForPlayer(playerid, i, 0xFFFFFFFF); // white colour, change it to what you want to set it back to normal
        ShowPlayerNameTagForPlayer(playerid, i, true);
    }
    return 1;
}

You need to loop all the players online to stop them from viewing a particular player marker. Else, you can do what RedWolfX said and just stop any viewable features of player markers.