In Tin Pan Alley songwriters used to play their compositions to the ‘old greys’, the elderly doorkeepers and other employees in the offices of their musical publishers.
If the ‘old greys’ were still whistling their tunes after a week or two they were likely to be worth publishing.
They would be reckoned to have passed ‘The Old Grey Whistle Test’.

I always wondered what whispering Bob Harris was on about.

Thank you Mr. Brewer for that little gem.