In case your not familiar with them, book curses* are my favorite and perhaps the only non-physical way outside of basic human decency to protect your books from theft. I’ve recently acquired (through honest means) two books** that employ book curses, one blatant but rife with grammatical complications, and the other a bit more subtle but all the more menacing:
My as-is transcription: “Dont Steel This Book My Onest Frends for fear the gals Will be En(?)d” – ‘gals’ I think is short for gallows, though originally I thought it was ‘gods’ – see below.
I had a really hard time transcribing the first and more overt of the two, but I believe it to be poorly spelled and abbreviated variation of the somewhat popular medieval book curse:
Steal not this book my honest friend
For fear the gallows should be your end,
And when you die the Lord will say
And where’s the book you stole away?
The second of the two, though more of a borrowing limit than a curse, by employing a patchwork of bible verses at the very least hints at an unspoken ‘OR ELSE’ should the borrower not respect the heaven-ordained limit.
So, if you’re feeling adventurous, just let me know and I can lend it to you for 15 days and we’ll see what happens.
 Murray, Stuart (2009). The Library: An Illustrated History. Skyhorse Publishing. p. 41.
*Here’s a nice article article I dug up that discusses book curses: https://medievalbooks.nl/2015/07/10/chain-chest-curse-combating-book-theft-in-medieval-times/
**Also, my two books containing the above-mentioned curses, in order of their photographs:
J. N. Select Lessons in Prose and Verse, from Various Authors, Designed for the Improvement of Youth. 11th ed. London: Howard & Evans, 1807. Print.
Hort, W. Jillard. The New Pantheon or an Introduction to the Mythology of the Ancients for the Use of Young Persons to Which Are Added an Accentuated Index. London: Longmans, Green, 1867. Print.