Joshua Bell plays the DC Subway

The story is here. (Includes video clips.)

Only one person recognized him:

As it happens, exactly one person recognized Bell, and she didn't arrive until near the very end. For Stacy Furukawa, a demographer at the Commerce Department, there was no doubt. She doesn't know much about classical music, but she had been in the audience three weeks earlier, at Bell's free concert at the Library of Congress. And here he was, the international virtuoso, sawing away, begging for money. She had no idea what the heck was going on, but whatever it was, she wasn't about to miss it.

But one other person recognized that something special was happening:

Like all the passersby interviewed for this article, Picarello was stopped by a reporter after he left the building, and was asked for his phone number. Like everyone, he was told only that this was to be an article about commuting. When he was called later in the day, like everyone else, he was first asked if anything unusual had happened to him on his trip into work. Of the more than 40 people contacted, Picarello was the only one who immediately mentioned the violinist.

"There was a musician playing at the top of the escalator at L'Enfant Plaza."

Haven't you seen musicians there before?

"Not like this one."

What do you mean?

"This was a superb violinist. I've never heard anyone of that caliber. He was technically proficient, with very good phrasing. He had a good fiddle, too, with a big, lush sound. I walked a distance away, to hear him. I didn't want to be intrusive on his space."

Good fiddle, yeah. That would be a 1713 "golden era" Strad.