My Grandfather's watch fob

This was my paternal Grandfather's watch fob. My Mother wore it on a chain as a necklace and I inherited when she passed away. I never thought much about it, but have grown to love it and would love to know anything about it. All I know is their purpose and some where fancier than others. There seem to be hallmarks, but they are impossible to read. I tried to take a picture, but so far no good results...would also be interested in finding out it's approximate value for insurance purposes.