[Calabresi]

There must be a variable that shows the faction of the player, for example PlayerInfo[playerid][pFaction], and another variable that shows the faction of vehicle, for example VehicleInfo[vID][vFaction]. Then, all you gotta do is;

pawn Код:

public OnPlayerEnterVehicle(playerid, vehicleid, ispassenger)
{
     if(VehicleInfo[vehicleid][vFaction] != PlayerInfo[playerid][pFaction])
     {
          new msg[128];
          format(msg, sizeof(msg), "You are not member of faction %d!", VehicleInfo[vehicleid][vFaction]);
          SendClientMessage(playerid, -1, msg);
     }
}

Just to give the idea.