Originally Posted by duckduckgoose

Bookmarks are typically done on the client side alone, with no server-side involvement, so there isn't really any consistent way to determine if a user has bookmarked a given webpage.

Having said that, there is some Javascript that you can use (in Internet Explorer only) to prompt the user to bookmark a given webpage in their web browser. You could theoretically have the user click a link which recorded their bookmark request, then once that is completed, output the javascript to prompt them to actually do the bookmarking. However, since this is Internet Explorer only, it is not recommended, and also most users bookmark pages wherever they want, not by clicking a link to bookmark pages.

So, in short, there isn't a reliable, consistent, cross-browser way to determine this.