Is the Series 2006 A $100 bill supposed to have a small number on the reverse?

First, let me apologize for making my first post here in six months a question instead of contributing to another conversation somewhere on the board… it’s been an interesting time for me lately, and I haven’t had as much time on the internet in general for the past few months. I hope I get to spend more time on the SDMB in the future.
I recently received a $100 bill from my mom to help with gas money on an upcoming family vacation, and I noticed something while I was looking it over. On the reverse, underneath the ‘100’ in the top left, there is what appears to be a very small ‘9’ in a reddish color. I think it’s just a piece of red fiber that happened to get curled into the shape of a ‘9’ because there are other red fibers nearby on the bill, but my wife thinks it’s supposed to be there. I’m having trouble finding detailed information on that series of $100 bills (as I mentioned in the thread title, it’s a Series 2006 A, and it has the Cabral-Paulson signatures), because they’ve been replaced by a new design now. So does anyone have a $100 bill from that series handy (I realize just what it is I’m asking here, btw), or have any more information on that series of bills? Is there supposed to be a number there, or is it just a funny coincidence?

There’s a fairly high-resolution scan of one on Wikimedia Commons. It doesn’t have any numbers under the top-left 100.

Almost certainly a coincidence.

Holy cow, that is “fairly” hi-res? That was amazing!
It makes me wish I could scan the $100 bill that I got with the same kind of clarity… just because I think it’s interesting how much it looks perfectly like a 9.

Did you ever see the back of a $100 bill… On WEED?