During the Second World War the BBC news was preceded with the opening bars of Beethoven's Fifth played on a kettle drum - because the beats are the same at the Morse Code for 'V', and so the broadcasts were seen to be sending out the message 'V for Victory'.
And composer Ronnie Hazlehurst, who wrote loads of TV theme tunes, spelled out the words Some Mot(h)ers Do Have 'Em (the 'h' is missing) in the theme tune of Michael Crawford programme.
There must be more - and I be fascinated to hear about them.
If my memory serves the code in the "Morse" theme tune actually spells out his first name which was a matter of some debate at one time. Im not sure of the spelling but his name is "Endeavour".
I dont know of any other instances.
Elgar's 'Enigma Variations' is also supposed to have an hidden theme running through the movements, but no-one has ever found it, although there has been lots of (quite dull) scholarly debate on the subject.
Ronnie Hazlehurst was challenged by the writer of the Michael Crawford sitcom 'Some Mothers Do 'Ave 'Em', Raymond Allen, to make the theme tune spell out the title in Morse code. And it does, not counting the apostrophes. THAT was a while coming, wasn't it...
(Apologies - that doesn't answer the main question - I found the second part about the Mars piece while searching google and responded before I realized his wasn't on topic. (D'oH.)