Bell: What are you doing?
Sherlock: [has two bikes with him] These were chained to a lamppost down the street.
Bell: And you figured you'd... steal them?
Sherlock: I'm re-stealing them. I peruse the crime blotter when I'm bored, and these were stolen in Chelsea last month.
Bell: And you're just gonna walk around with them for the rest of the day?
Sherlock: Don't be ridiculous. This one's for you.