downloading signed programmes?

[andrea]

Hi

I would like to download

The Apprentice: Series 8 - The Final: 14. Interviews, Signed, Entertainment,Reality,Sign
Zone,TV,Talent Shows, signed


but I get

INFO: 1 Matching Programmes
WARNING: No programmes are available for this pid with version(s): default (signed are available)


I can still watch it on the BBC iPlayer website. It is the version for hearing impaired people.

What is this "signed" thing?