I think collecting bottles is one of the most interesting parts of collecting. There are so many different types and shapes that each one is a work of art from the past. I'm not too up on specific bottles, but here's what I can tell you.
That (I) between the 20 and 68, which I am assuming is an I with a circle around it, indicates the bottle was manufactured by Owens-Illinois Glass Co. which is in Toledo, Ohio. Bottles that were 10 ounce with the no deposit no return were made in the mid-1960's. The most common had a diamond shape Coke logo embossed on it. Others around that time had a paper label and could have been clear or green. The clear bottle was more common. The ACL or Applied Colored Labeling was also used. A mint condition bottle like this could be worth up to $150.