I’m not sure what you’re trying to say. How are ratings “vanity plates”? How are they ineffective?

They’re ratings. They tell the viewer what type of content to expect so they can judge if it’s appropriate. That’s what ratings are for. They’re as functional as any other label.

In the 90s, the FCC absolutely wanted to get involved, off the heels of Tipper Gore’s (she was the Vice First Lady, which held more of a cultural tone-setter role here in the US up until the mid-00s) efforts to “protect the children”. The US has long history of government agencies and law enforcement enforcing “decency” laws and ordinances over film, TV, radio, and music. In almost every medium (except arguably radio), an advocacy group was formed, pooled their influence, pushed back, and ended up forming a voluntary ratings board (ESRB, MPAA, parental advisory labels, etc etc).