I believe that they are pure silver. I do not know of any law that states that items made of silver must be marked as such, it would just make it easier to know the composition if it was marked. There are many examples of items made of silver but not marked as such like the earlier Hard Rock Casino Silver Strikes that were won in machines, souvenir tokens that were made with the same dies that the dollar slot tokens were created (casinos would not altar the dies to make these souvenirs).