Make Busking Historic.
The Dualers are buskers. They're not famous as far as I'm aware, but their professional set-up in terms of microphones and amplification had drawn a crowd. So far so normal. They also sold CDs. Less common but not out of the ordinary.
But what was unusual was the way they vociferously offered to sign the CDs. And it worked. To some people, they had made a run of the mill busking CD seem special. Now that's what I call marketing.