Steve,
The "O" in the square was dubbed the "Box O" mark by researcher Bill Lockhart. The mark is of the Owens Bottle Company of Toledo, Ohio and was used from 1911 to 1929. The company has changed and is today OI Corporation. See oi.com
Bill identified dozens of embossing variants. It is likely but not certain that the 6 refers to Plant #6 (Charlestown, WV) and the 7 is a date indicator - here it would mean 1923-1927.
Generic bottles like this with no company embossing on the body of the bottle are darn common and are really not worth that much, if anything. These were made by the thousands for use by pharmacies and companies. Add Label - Have Product.
