ahkai
It looks like this note has been stained with red colour. Most likely, someone left this note in a red package in their clothes and then took it for a wash. Must be more than one note in the package and that is why only one part is showing a much stronger stain than the reverse. I have seen such notes before (with red stains).
+1
Definitely looks post-production damage to me. The clues? Design of the note is faded (likely from bleach). Its possible the dye, juice, etc spilled on a pair of pants, seeped into the note & the pants were put in the wash. Areas where the dye seems to be missing could be from a money clip, coin or some other object which protected the note.