Puzzle 1: Let's Go!

In 1915, Detroit police sergeant Harry Jackson created the first stop sign.

While working traffic duty at a busy city intersection, Harry found he was always having to slow the traffic from one particular street that had poor visibility entering the intersection. To make his job easier he took a piece of plywood, cut off the corners to make it more distinctive, and wrote "STOP" in the center. He placed his stop sign facing the street and found that it really improved traffic flow at the intersection.

Harry shared his idea with other officers and the signs quickly spread across the city and then the state.

Wikipedia: Stop sign