I know they are made for using on glass, but has anyone ever tried them on silver?

They can be used on enamel to add another layer. They are very good to sign enamel. They are not designed to use on metal without other enamels. Although it is not impossible, used alone they would likely flake off.

 I like the idea of signing my enamel work or drawing pictures. Thanks :)

I use vitrea160.  Comes in pens and jars of paint.  While designed for glass, they will work on fine silver.  After applying, you need to bake at 325 degrees F for 40 minutes.  According to their literature they are dishwasher safe after baking, though I have not tried this with the jewelry.  Available at Michaels, Hobby Lobby, and online at *** Blick.

Bob