[DobbysGamertag]

Add a boolean to your script

pawn Код:

new bool:IsNew[MAX_PLAYERS];

//somewhere you check if they've registered. EG, showing a register dialog.

IsNew[playerid]=true;

//Actually adding the account, or making them "not new".

IsNew[playerid]=false;

//example
public OnPlayerSpawn(playerid)
{
    if(IsNew[playerid]==true)
    {
        SendClientMessage(playerid,-1,"Welcome.");
        IsNew[playerid]=false;
    }
    return 1;
}

Hope it helped