The Mercury is in a glass tube with two wires and the tube is attached to the bimetallic strip in such a way that the motion of the Mercury due to gravity as the strip moves will close the circuit between the two wires. The Mercury is just being used a liquid conductor.
Not sure what counts as ‘regular’ circulation. But there’s a Canadian ‘toonie’ in circulation that has a glow in the dark Aurora on it. https://www.google.com/amp/s/www.cnbc.com/amp/2017/06/27/canada-released-glow-in-the-dark-coin-150-year-anniversary.html