Score another for philately!
Bruce looking at his collection was shown in the second season (1967), episode 51, and confirmed after the first-day ceremony by the current comic book co-editors. You can read the story here.
One place to watch the episode, “A Piece of the Action,” is here. I did not find it on YouTube.
Stamps have been shown on different tv series. Just last week, I saw an episode of Poirot, and he collected stamps as well