I have run across the M.R. marking on vintage items on several occasions, but when I saw it embossed in glass the first thing I thought of was the MR Hemi 42. This pic is of an old Oster Deluxe blender with a copper base. I think on it and the other items the M.R. is for "Mark Registered" which has been replaced by the T.M. and/or R in a circle. Of course I don't think there is any correlation to the insulator, since the marking is usually quite small, it has periods because it's an abbreviation, and it occurs on items that are later in production (late 50's to early 60's) than the MR insulator, but still I did a double take when I saw this. The search for one of those overlooked Hemi's continues...