Signed, your neighbors is a paper note in Fallout 4.
Location
The note can be found at Hyde Park, on the tallest rooftop which is towards the most southern end of the town, pinned to a mattress with a combat knife.
This note could be from the Gunners, located at Gunners plaza, from the raiders at Quincy Quarries led by Slough or from the raiders inhabiting Hyde Park themselves to the previous residents, due to the number of settler corpses strewn around the buildings.
Transcript
Looking forward to seeing you.
Signed,
Your Neighbors
Gallery
The note, in Scutter's shack.