I am trying to identify this bottle. It is thick glass with a couple air bubbles. Centered on the bottom is an indented circle with a smaller circle inside it and what looks like a small plus sign inside of that. There is also some faint numeral/letter markings that I' m guessing read: 6AD MI. It is also much thinner on one side of the bottom where the air pocket dips down nearly to the base. (opposite side of the picture) Any assistance is greatly appreciated. Thanks!