The 9 digits are based on your Sky card viewing number, albeit changed with a calculation (presumably only known to Sky).
The numbers are part of Sky’s attempt to try and stamp out piracy of its channels on the internet, and to see which pubs are using a private subscription and not a publican subscription which is indicated by a pint glass symbol.
As internet streaming and card sharing becomes more popular, where just one sky card can be viewed by many, by displaying the viewing card number on the screen or feed, Sky can see which Sky card is being used for sharing the programme content over the streaming websites, and deactivate that card. Similarly “mystery Drinkers” can see which pubs are using a domestic subscription and not the more expensive Pub subscription.