Hill of beans

Hi all
I recently came across the following reply in an (American) play:

'Beaty don't know nothing! Hills of beans have flags in them announcing what Beaty knows!'
Beaty being a particularly stupid character in the play. I know that "hill of beans" means something like "nothing at all" or "worthless", but I was wondering about the "flags" on them - do they make the insult worse in any way? Or am I completely mistaken about the meaning of this idiom?
Grateful for any hints.
Cordially
Joachim