The melody, with the possible exception of the dotted-eighth/sixteenth rhythm at the start of each line, is in the public domain as it was published prior to 1922 with the lyrics
Good morning to youI am unaware of any copy of the Happy Birthday lyrics having been published prior to 1922, though I've read that at least one pre-1922 publication of the work noted that the song was also titled "Happy Birthday to You" but did not explicitly write out the lyrics. It would seem likely that might be sufficient evidence to disqualify the claimed copyright on the lyrics, but a cartoon in 1935 (Ub Iwerks' Mary's Little Lamb) uses the tune (without lyrics) in such a way as to suggest it was primarily known with the "Good Morning to All" lyrics.
Good morning to you
Good morning dear ____ [or dead Children]
Good morning to all
That having been said, I'd like to see a restaurant use something like:
Your birthday's today.BTW, that latter point reminds me--I have on occasion heard restaurant staff singing made-up birthday-song replacements to tunes which, while their origins may not be well known, are more recent than "Good Morning to All" and are, in fact, still under copyright.
What more can we say?
The tune's out of copyright
ASCAP go away.