It's the second-highest honor that an artist can receive for enriching French culture.
The title, which isn't strictly limited to French artists, is given to those whose work has greatly enriched French culture. It's not Mills' first time receiving honors from the country's Order of Arts and Letters—in fact it's a promotion from Knight, the lowest of three rankings (which he received in 2007), to Officer, the second-highest order. Other artists who have received an Officer's medal include Pharrell Williams, Elton John, Tim Burton and Jim Jarmusch.
Mills was also honored by the Detroit City Council last year for his "outstanding achievement or service" to the citizens of his hometown.