A Letter Found on a Dead Body can be found by looting a body just west of the Broken Bridge landmark in the Hinterlands. Reading the note initiates the side quest Return Policy.
Note text Edit
TAKE IT BACK TAKE IT BACK TAKE IT BACK
Dreams won't stop until you take it back to the
They will never stop
You will wake up screaming and find notes
written by your own sleeping hand
TAKE IT BACK
Or i will draw allies to do it for me
Note: This note is not included in the Codex.