These bumpers are the most well known as they usually were animated with the Icon Ghost doing something before stating "We're be back after these messages" or "We now return to the Real Ghostbusters". Later seasons went to an almost Ident Bumper type with only audio announcer. Network Bumpers can be found here.
These bumpers acted much like Break Bumpers, except they were a still of the logo for the show and music of the show. These were mostly used during the middle of the hour formatted broadcasts to keep the viewer waiting.
Not to be confused with RGB ads, it was used to promote that the show "has more to come". Usually these could be seen in at the end of the first episode of an hour block. They were used second half of Season 3 to the end of Season 6. It would show clips from either one show or a number of shows, and state they are coming back.
Note that we count Syndicated as Season 2, and ABC year 2 as Season 3.
In Ghostbusters International #2, on page 15, in panel 5, to Ray's right is small frame with a grab from The Real Ghostbusters bumper when the Icon Ghost is leaning against the logo whistling and does its "We now return..." line.