[NeuZz]

pawn Код:

new TieneObjeto[MAX_PLAYERS];//arriba de tu gm

if (newkeys & KEY_SUBMISSION)//en la callback
{
    if (IsPlayerInVehicle(playerid, sunrise1) && gTeam[playerid] == TEAM_FBI && GetPlayerState(playerid) == PLAYER_STATE_DRIVER)
    {
        if(TieneObjeto[playerid] == false)
        {
            AttachObjectToVehicle(myobject, sunrise1, -0.599999,0.075000,0.750000,0.000000,0.000000,0.000000);
            TieneObjeto[playerid] = true;
        }
        if(TieneObjeto[playerid] == true)
        {
            DestroyObject(myobject);
            TieneObjeto[playerid] = false;
        }
    }
    if (IsPlayerInVehicle(playerid, sunrise2) && gTeam[playerid] == TEAM_FBI && GetPlayerState(playerid) == PLAYER_STATE_DRIVER)
    {
        if(TieneObjeto[playerid] == false)
        {
            AttachObjectToVehicle(myobject, sunrise2, -0.599999,0.075000,0.750000,0.000000,0.000000,0.000000);
            TieneObjeto[playerid] = true;
        }
        if(TieneObjeto[playerid] == true)
        {
            DestroyObject(myobject);
            TieneObjeto[playerid] = false;
        }
    }
    if (IsPlayerInVehicle(playerid, sunrise3) && gTeam[playerid] == TEAM_FBI && GetPlayerState(playerid) == PLAYER_STATE_DRIVER) //DestroyObject(myobject);
    {
        if(TieneObjeto[playerid] == false)
        {
            AttachObjectToVehicle(myobject, sunrise3, -0.599999,0.075000,0.750000,0.000000,0.000000,0.000000);
            TieneObjeto[playerid] = true;
        }
        if(TieneObjeto[playerid] == true)
        {
            DestroyObject(myobject);
            TieneObjeto[playerid] = false;
        }
    }
}

Con una variable booleana se puede hacer, arriba te lo deje echo (: