I am looking for a similar answer. My mother has a fork with a start stamped on the back then it says Rogers&Bro. then IS. I figured that IS stands for International Silver and that the company started in 1847. They later introduced a line of silver plated flat wear. I can find all kinds of info of the silver plated stuff, but nothing with a star stamped on the back.
Wm Rodger*(star stamp) IS on a flatware means that the international silver bought the rights. This took place in 1989 and still applies to every product of the flatware. Check out the legalized form at http://www.examiner.com/article/rogers.