1 it has mandolin on it
2 it can be played really fast
3 everyone is wearing hats
4 everyone is hovering around one mike
5 BILL MONROE ever touched the song
6 it sounds like Irish music with a southern twang
7 someone is singing ridiculously high and lonesome
8 less than six chords probably no more than three
9 If it has ever been played in Kentucky
10 if the singer wants beef steak, whiskey, and sweet heaven when he dies
if the song has 8 to 10 of these traits IT'S BLUEGRASS
5 to 7 more than likely
4 or below it aint unless it was written by #5