PDC, I don't think that is used any more.
If I remember correctly this was a coding signal (encoded with the teletext signal?) that VCRs could pick up when programmed using VideoPlus codes, if the programme started late then the video would wait.
It worked too, I used to have a VCR with it, and it was good, but I don't think it's used on any digital platform.
Actually:
http://625.uk.com/pdc/