Set of Six Unusual Oriental Enamel Bookmarks

I am offering these six bookmarks as a set. The enamel is in very good condition.  They measure 2 3/8" high x 1" wide.  The top three appear to be masks of some sort; they are marked "Chang Fei", "Chang T'ien-Shih", and "Sun Wu-K'ong".  The bottom three are marked "Longevity", "Prosperity", and "Good Luck".  They are made of some sort of very thin metal, showing some discolorations which I have not attempted to clean, I am leaving them "as found".  The buyer may polish if you like.  The red one for Good Luck has a very slight bend in it.  There is nothing on the reverse side. Unusual...