The UK Office of Public Sector Information has released the Bunnyfoot User Testing Report: OPSI—Crown Copyright.
Here's an excerpt:
75% of respondents did not recognise this image [Creative Commons Attribution License symbol].
Lack of recognition was highest amongst the "general public"—87%. And lowest amongst respondents from the OPSI website—55% did not recognise the image.
The majority did not understand the meaning of the image. Understanding was highest amongst the OPSI website respondents—35%.
This is not surprising as this group was also the group in which the most had heard of Creative Commons licences before—47% (vs 10% of the "general public" and 29% of the OPSI database).
Only those likely to be more familiar with copyright (inferred from their route to the survey) are likely to have a previous understanding of Creative Commons terminology and imagery. One might argue that if these are used moving forward, more people will become more familiar with these, however, the benefits at this stage of shared/added meaning would only really apply to a minority—a minority who are likely to have a strong understanding of Crown copyright already.