Any idea to what this might be worth?

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I just went through a bundle of circulated 20's and found this note.  The color looks like a color used on the banknote, but is only on the left side of the note.
The back of the bill is perfectly fine....and it doesn't smell like coffee

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I'd say dirt or some other substance, especially since it's circulated. Of course, this is without having seen the note in-person.

Looks like dirty at firs but has fairly straight lines with a pink/orange hue. Difficult to tell without seeing it up close.