Thumbscan
From Memory Alpha, the free Star Trek reference
A thumbscan is a biometric identification consisting of an image of an individual's thumb print. The process of obtaining this image is also called a thumbscan. It is often used to record one's participation in a contract, presence at an event, or acceptance of an agreement.
In early 2370, a Cardassian Gul put his thumbscan on a Kressari PADD after delivering several weapons to them. (DS9: "The Circle")
Kira Nerys later displayed the PADD with the thumbscan before the Chamber of Ministers. (DS9: "The Siege")
Later that year, Quark tried to get Inglatu's thumbscan, thus making the contract between the Ferengi and the Dosi official. (DS9: "Rules of Acquisition")
