http://bulbapedia.bulbagarden.net/wiki/Trainer_card_(game)
In Generations III and IV, the Trainer Card also carries the Trainer's score. A Trainer's score offers no specific purpose in the game and appears to be only aesthetic. The score begins at zero and increases every time a score-altering event occurs.
Event Change
Berry is picked +1
Battled against a wild Pokémon +2
Battled against a Pokémon Trainer +3
Pokémon Egg is hatched +7
Pokémon is traded +10
Pokémon is evolved +20
Flag is obtained in the Underground +34