signed in blood : Java Glossary

In novels, people make pacts with the devil by signing the contract in blood. I suggest a lighter weight scheme for signing important contracts like rental agreements, house sales, car sales etc. Both parties sign, then put a small drop of blood next to their signatures on each copy of the document. This drop can be used to help verify the signatures. With DNA (Deoxyribonucleic Acid) testing, they can also be used to identify who signed a document under an assumed or completely fictional identity. For example, this would make renting out properties not owned a more difficult crime to get away with. You might devise a signing device that would make it difficult to substitute the blood sample.

You could use a donut-shaped plastic seal to indicate where to put the blood drop. It would keep the drop in a tidy circle. You could blot off any excess from the slippery surface of the seal. The seal might also give some indication what it is for with a logo and website.