Lyric discussion by DBMcGee 

Cover art for The Front Porch Song lyrics by Robert Earl Keen, Jr.

I don't think it is "G's and R's and X's"

I'm pretty sure the lyrics are: "It ain't never seen or heard the day of GNR and INXS." Meaning POP and Hard Rock music.

@DBMcGee, the line is referring to the movie rating system. He's singing about a closed movie theatre which still has the poster from the last movie it showed. "Giant" was a movie that starred Marilyn Monroe and James Dean, and it came out in the sixties, before movies were rated G, R, or X.

@DBMcGee Also, this song was written by Lyle and Robert Earl in the 70's. GNR didn't exist until the 80's.