does anybody know what this is and when it was made

I have no idea what this but it was givin to me buy my grandma,she said it was very old I have been trying to fiqure this out for around a year but no luck hopefully there is someone knowledgable in this matter out there that would help m e out.it is about 3" tall 2 1/2" dia.
has the letter "M" stamped on the back pleaser if anyone know what this color glass is called when you would date or just any good glass referance wbsite please call me at 330-771-1807 or email me therareones09@gmail.com

thanks so much happy holidays