It's a (vintage?), Sears, Roebuck & Co. Surrey Milk Glass Coffee Mug (3¼ inch tall x 3⅜ inch diameter. I also have the same format mug, but it's ceramic that I use as a shaving mug.)!
I do not drink coffee or tea, but in my experience in the army found those folks who left their coffee cups age had very little trouble finding their cups. Those who were C3, Compulsive Cup Cleaners, always had to go looking for their cups. I guess a bit of grunge turns folks off and they will leave your stuff alone.