Per Pokémon wiki
Ash's first hat, worn during the original series, is easily the most well-known: an official Pokémon League Expo hat that was red and white with a green, stylized "L" on the front, which Ash claimed to have "sent in about a million postcards" in order to obtain. Misty seems to have tried to win it as well, as she stated she sent in one postcard. Ash wore this hat during his journey through Kanto, the Orange Archipelago, and Johto, and was very attached to it, becoming enraged when a Mankey stole it and played keep-away with it in Primeape Goes Bananas. The design may be loosely based on Red's Generation I hat, and in early concept sketches for the anime, Ash's hat matched Red's exactly.
Från Primeape Går Bananer (25: e avsnittet av den första säsongen)
Misty: I didn't know that was an official expo hat. I remember entering the same contest myself.
Ash: I had to send in a million postcards to win that hat!
Misty: He he. No wonder I didn't win, I only sent in one.
Intressant var att hatten gick igenom flera iterationer innan konceptkonstnärerna äntligen bosatte sig på "L" -symbolen. Tyvärr är min japanska otillräcklig för att dechiffrera texten på höger sida längst ner.
