Halford's note contains the schematic for the dog tag fist. Based on the conversation with Private Halford, the note apparently pertains to the lakelurk threat in and around Camp Guardian. He wants the Courier to take the note to his (former) NCR superiors and convince them that the threat is real.
Private Halford hands the Courier the note if the Camp Guardian caves are successfully cleared of lakelurks.
I've found it possible to create a sort of makeshift weapon using all of the dog tags I've been collecting over the past month. One of these days the NCR is going to pay for their continual mismanagement and idiotic bravado.
<On the backside of the page is a schematic drawing of the dog tag fist weapon.>