A Content Rating System for Casting Calls

While yes the site does have a R+18 option. But there are projects that are not quite explicit enough for an R+18 but can still be considered NSFW. How about a way to give your CC a rating system such as…
G- Perfectly clean & kid friendly.
PG- Occasional mildly explicit content
PG-13- Considerable amounts of explicit content but nothing overly graphic.
R-18- Plenty of rather graphic content
Or something like that.