The first thing to look for is the fluid ounces. Normally this is embossed onto the glass bottle itself; the plastic ones tend to have this information printed on the label which would come off if kept over long periods of time. The content can be measured in terms of ounces, fluid ounces or even milliliter, depending on the location where the bottles are produced.
Then there is the shape of the bottle itself. There is iconic “hobbleskirt” or the tall straight sides ones. Or the short wide ones which narrow at the top.
The other things we would look out for is the printing on the bottle itself, at its center. It could be the regular Coca-Cola script writing or a banner produced to commemorate a special event. These events include special occasions like the Olympics, Nascar race, Super Bowl, etc. Other limited edition bottles are produced for the some celebrations like Christmas, Mardi Gras, etc. There are special Coca-Cola glass bottles that can be found in a specific location like Disneyland, Movie World, World of Coca-Cola, etc.
As for the regular Coca-Cola script bottles, each country will produce their own Coca-Cola logo which is in the local language. Therefore you can find Coca-Cola logos in Chinese, Thai, Arabic, etc.