Unusual marking on $20 bill

This looks like it was done at the mint, I'm no expert so I'm not sure.  I would like to know if this common and if anyone has info on it.

By looking at the condition of the note and comparing the mark on the note, I am not convinced that this was done at the Mint. I cannot say what those letters/number are for, but I have a feeling that it was stamped privately. I could be wrong. 😁

Counting houses which change cash for foreign currencies often add marks to notes. This may be such an instance.

I have no idea, but holding it in your hand and looking at it, the mark “appears” to be very much like the ink of the printed bill.  Hopefully someone can positively solve this.  Thank you for your feedback.

Just because it's black? What about the fact that it's upside down and unaligned (at an angle), the ink is bleeding quite severely etc.?

Ockham's Razor → some random after the fact addition by a third party be it an exchange house, casino, a drug gang or terrorists or some random dude with to much free time and a rubber stamp.
 

Idolenz, not just because it's black, and under magnification there does not appear to be bleeding of the ink ( you seem to be seeing something that's not present).

I see quite a bit on the $, C and a little bit on the 4 in contrast to all the other lines and letters on the note. But even if I were wrong all the other stuff still stands.

I'm looking at the note with a magnifying glass and do not see any perceptible bleeding.  As for the other things, who knows, that's why i asked hoping to get a knowledgeable answer from someone who may have seen the same thing on another note.

Vetz76

from someone who may have seen the same thing on another note.

That no one has should tell you all you need to know.

Well I suppose everyone on this forum has seen my post, apparently that’s what you’re saying.