What is Pricking For Sheriffs?

Legal Definition
In England, when the yearly list of persons nominated for the office of sheriff ls submitted to the sovereign, he takes a pin, and to insure impartiality, as It is said, lets the point of it fall upon one of the three names nominated for each county, etc., and the person upon whose name it chances to fall is sheriff for the ensuing year. This is called "pricking for sheriffs." Atk. Sher. 18.
-- Black's Law Dictionary