The only way you can get people to bookmark your site is not telling them to bookmark your site. The only way to get people to bookmark your site is to give them valuable content – give them something interesting enough to read, see, hear and experience. Whether people bookmark your site or not is not in your hands. You can only offer them content they appreciate and hope for the best. It’s up to you to use links that say ‘bookmark this site’, but I bet that has little or no influence on the user’s decicion. It’s only couple of clicks from the bookmarks menu anyway to do.