Question about 10 Dollar Bill.

[CopperFinger]

I had a bill the other day were the serial # started out with a double BB and the numbers followed by B. Under the BB on top left serial# the BB had a B2 printed ina slightly darker color. The S# on lower left of bill started with BB followed by #s and a B. Ive never seen a bill starting with a double letter and was wondering if this was out of norm and what could be going on with this 10 dollar bill?