On his blog Got Medieval, Carl Pyrdum discusses medieval copy protection, which often manifested as a book curse "essentially the same as that little FBI warning that pops up whenever you try to watch a movie."
Pyrdum offers the following example from Yale's Beinecke MS 214:
In the name of the Father and the Son and the Holy Spirit, Amen. In the one thousand two hundred twenty-ninth year from the incarnation of our Lord, Peter, of all monks the least significant, gave this book to the [Benedictine monastery of the] most blessed martyr, St. Quentin. If anyone should steal it, let him know that on the Day of Judgment the most sainted martyr himself will be the accuser against him before the face of our Lord Jesus Christ.