It's a more than just 2 block letters, a lot more.
I see some arrows and testimony that mentions (for the order blank itself) only a letter A, a letter D (which by the way is different on the envelope), and a letter x. So, my bad -- unscientific and biased handwriting "analysis" of
three block letters on a photocopy of a microfilm copy of a two-inch order coupon. From microfilm that is conveniently "missing".
Edit: actually if you read it again, it's ambiguous but it looks like he's only referring to the envelope when he talks about the "A", "D", and "x".