When did ratings come on tv shows?

Answer 1

1997- In 1996 congress asked the television industry to establish a voluntary rating system for TV programs. In response, the National Association of Broadcasters, the National Cable Television Association, and the Motion Picture Association of America created the rating system known as "TV Parental Guidelines." On July 10th, 1997 an announcement was made public that networks were to begin rating programming by Oct 1st, 1997 using the new universal rating system. In addition, the industry had agreed to begin encoding and transmitting these ratings in line 21 of the vertical blanking interval within 180 days of the agreement.