Along with the new TS-E lenses announced this week, Canon also revealed in the body of the press release, that they have updated their range of circular (hence "C") polarizer filters.
Extracted from the press release on Wednesday:
Canon today has also introduced a new range (52mm to 72mm) of versatile, multi-functional PL-C B polarizing filters to help reduce reflections from glass or water or darken blue skies. The PL-C B’s, which are now available in 52mm, 58mm, 67mm, 72mm, 77mm and 82mm filter thread sizes, also allows the lens cap to be attached to the lens to prevent damage to the filter if left attached when not in use.
Quite how they differ from the previous range, which we use here, other than being able to retain a lens cap isn't mentioned. Perhaps that's the only difference. I will ask them for clarification tomorrow at the Focus on Imaging trade show.
There also appears to be a typo in the press release, but we assume they mean the new range covers filter threads from 52mm to 82mm.