Found on the web............
While it’s tough to pinpoint exactly where the tradition of sporting fuzzy dice on the mirror originated, there is a good theory. During World War II, pilots would carry good luck trinkets with them aboard their aircraft. Gambling items like dice, cards, and chips were popular tokens of good luck because if they brought you luck at the gaming table, they could bring luck while flying a dangerous mission.
After the WWII pilots returned home, the tradition of carrying dice for good luck was translated into hanging them from your vehicle’s rearview mirror, and the fuzzy dice meaning continued to be for good luck. This was a trendy thing to do in the post-war boom, and it caught on quickly.