 Hip-hop musician Sean J.Z. Carter has become the latest celebrity backer of the online watch market after taking an equity stake in luxury trading platform Wrist Check. J.Z. participated in a recent funding round of about $5 million. The rapper joins a slew of other celebrity watch trading investors. Soccer superstar Cristiano Ronaldo and F1 driver Charles Leclerc are both investors in online watch trading platform Chrono24.