Narcotic tax stamp - a conventional U.S. revenue stamp with the overprint 'Narcotics', indicating that a tax has been paid on the shipment
Newspaper stamp - an impressed or adhesive stamp issued to prepay special rates for the sole purpose of mailing newspapers and periodicals
Nixie - a term used by Railway Post Office clerks to designate a piece of mail that cannot be sorted due to an illegible address. Such items were designated "dead letters" by other mail clerks.
No Sunday Delivery - a tab attached to the stamp indicating that the piece of mail was not to be delivered on Sunday. Removal of the tab indicated that Sunday delivery was allowed.