I mailed in my car insurance payment today, and used two 37-cent stamps. I used the envelope which came with the insurance bill, which had a plastic window in it for the return address.
The envelope also had a set of black vertical lines on the top edge, about 2.5 inches away from the upper-right corner. Five of them, covering a one-inch square. The lines were spaced somewhat like this:
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Because the stamps I used were rather oversized, they obscured these lines. If I had used normal-sized stamps, the lines would have been visible.
I assume these things serve some purpose - what is it? Should I be concerned that State Farm will never receive my payment because I’ve interfered with some system of theirs, or the post office?