new streaks[MAX_PLAYERS]; //global
public OnPlayerDeath(playerid, killerid, reason)
{
    streaks[killerid]++; //will add 1 to the killer's streak
    streaks[playerid] = 0; // will reset the streaks of the player who dies
 
    switch(streaks[killerid]
    {
        case :1
        {
            GameTextForAll("1 kill", 1000, 2);
         }
         case :2
         {
             //continue here
         }
     }
    return 1;
}