help me identify...

I just got cornered about a new book in the works here (I work in publishing). The opening page is an epigraph (a short inscription) quoting A3.

The editor said Hey I hear you know who this A3 is/are. What the heck does this mean: "I'm down with the Street Angels on this one" (I don't know if that's the exact wording - I left the manuscript at home). I had to admit I was at a loss. Any idea where this is from? I'm sure it's not a lyric.

Anyway, she is wondering if an average 17-year-old would be familiar with A3 (the book is aimed at young adults). My co-worker of course said "I don't think 17 people in North America know who they are".

I think they are going to kill the quote.