[Useless]

There is no way to measure who bookmarks your site. Awstats is looking at how many browser requests for your site's fav.ico there have been and is assuming that if the image is not requested, then it is already in the browser's cache - and then makes the assumption that that visitor must have been at your site before. Nothing to do with bookmarking at all. Also, not every browser handles fav.icos in the same manner. Just ignore that number and you'll be a happier webmaster.