Pedestrian crossing
Vending machine candy stuck
The Entscheidungsproblem originally posed by German mathematician David Hilbert in 1928. To which Alan Turing in 1936 has been called "easily the most influential math paper in history". page 
The Halting problem is often illustrated by a traffic signal crossing button. CS students may relate more to candy stuck in a vending machine.
Also, see - Tau Chain - Smart Contracts