forward HideNPCMarkerForPlayer(npcid, playerid);
public HideNPCMarkerForPlayer(npcid, playerid) {
    SetPlayerMarkerForPlayer(playerid, npcid, 0xFFFFFF00);
    return 1;
}
public OnPlayerConnect(playerid) {
for(new i = 0; i < MAX_PLAYERS; i ++) {
    if(IsPlayerNPC(i)) {
        HideNPCMarkerForPlayer(i, playerid);
    }
}
return 1;
}