As requested

 is a note that is found in the Hollowed-Out Rock south of Megaton, together with a Sniper Rifle and other useful items.


 * The "S" mentioned might be the character Sam Warrick, who roams the Capital Wasteland with a Sniper Rifle, usually hunting Wastelanders.
 * The phrase "Happy Hunting" may also reference Moira Brown who says that after ending conversation with her


 * the phrase 'If anyone asks where you got it -- say it was a gift from your grandma' could be a criptic reference to the G.O.A.T test in fallout 3 in which question 5 asks how you would react if your grandmother ordered you to kill 'another vault resident'.