"Hello World!" by Brian Kernighan, from Artsy's Algorythm Auction based on a 1974 Bell Laboratories internal memorandum, "Programming in C: A Tutorial," which contains the early version. It was reprinted in the popular 1978 book, The C Programming Language.
2 lines of C Code on acid-free dot-matrix computer paper, framed.
https://commons.wikimedia.org/wiki/File:Hello_World_Brian_Kernighan_1978.jpg