The only time I have heard this is in respect of Douglas Adams, and the book "so long and thanks for all the fish". I think it was in respect of the dolphins that went missing/returned to earth and the inscription was on a glass bowl.
It was a Douglas Adams thing, but it turned up earlier on in the series, I think in the Hitchihikers' Guide. When the earth was destroyed to make way for an interstellar freeway the dolphins - who, it transpired, were a higher life form than humans - jumped ship with the parting words 'So long, and thanks for all the fish'.
Yep. But only after they had attempted to warn the humans about the impending destruction for a long time. The messages were all misenterpreted as atempts to balance fish on their noses or catch footballs. The final "so long.." message was, if I remember, delivered in dolphin as a sophisticated attempt to do a treble backwards somersault through a hoop whilst whistling the Yellow Rose of Texas.