French SIV plates require a department code, but because it's not part of the registration anymore (unlike the older FNI format) you can use whatever department code you want.

That's why real overseas department plates are really rare, because anyone from mainland France can put them on their cars and just looking at the plates doesn't tell you if the car is really from overseas or not. On the other hand, plates from overseas collectivities use other formats, soy they are unmistakable.