.
 

..

I have had good luck by using epoxy glue. I heat the glue slightly, to much and it will harden, and work it in the back side of the crack with the flat of a single edge razer blade. I then use rubber bands to apply light pressure while drying. Bill ( super Glue works well also)

Scratched in markings likely meant something to a former owner- but not to anyone else.
JMHO.