Very few Newsagents would risk accepting illegal bets from customers but they often sold weekly tips (on commission) in little sealed envelopes supplied by tipsters such as E.T.
E.T. is boasting of large SP wins that he has previously tipped. Another tipster, Harry Hall has his own wins on another placard
"E.T." is probably an abbreviation for something like "Early Tissue" - (a tissue was the printed list of runners that the bookmaker puts on his board with the odds in chalk against each runner).
P.S. It's a wonderful photograph capturing a lost moment in time.
