Just after the Babu gives Kim his special Amulet of Secret Agent-ness, Kim stumbles on another member of the British Indian Secret Service. This guy happens to be in the train compartment where Kim is sitting with the lama and the Punjabi farmer whose son Kim has successfully cured of fever. He is dressed as an upper-class Indian man, and he claims to have been in a road accident… but Kim can see that the man's story doesn't match up with his particular injuries. Plus, the guy's got a Secret Agent Amulet around his neck—a surefire sign that he's not what he seems.
Once Kim reveals his own amulet, the man levels with Kim: He is Agent E.23, and he is on the run from some assassins who have tracked him down to this very train; Kim uses his superior disguise skills to help E.23 escape. Later, when the Babu seeks Kim out to ask for his help against the Russian agents, the Babu mentions that E.23 is deeply grateful for Kim's assistance—grateful enough to tell his bosses what a great agent Kim is becoming. So Kim is gaining a positive reputation among the members of the British Indian Secret Service, at least, even if his work has to remain anonymous and hidden for the most part.