This is apparently a notice pinned up in the college library at Peterhouse, Cambridge. It is a Curse against Book Stealers, originally attributed to the Monastery of San Pedro in Barcelona. It reads as follows:
"For him that stealeth a Book from this Library, let it change into a Serpent in his hand and rend him. Let him be struck with Palsy, and all his members blasted. Let him languish in Pain crying aloud for mercy, and let there be no Surcease to his Agony till he sink to Dissolution. Let Bookworms gnaw his Entrails in token of the Worm that dieth not, and when at last he goes to his final Punishment let the flames of Hell consume him forever and aye."