Device information thru webbrowser

Question

I am looking for unique identifiers within webbroswers to pinpoint whom the browser is dealing with on a mobile device. My questions is, is there (apart from screen size information) any other information available or not available when using a web browser on a mobile iOS or Android devices compared to a browser on a pc or mac?

I have googled this a while, but can't really find anything helpful. Any links/references would be appreciated.