Older soda bottles made of glass often have manufacturing marks that indicate the company, site and potentially date of manufacture of the bottle. These marks often include a specific trademark symbol associated with the manufacturer along with other information in a coded form, but specifics vary from bottle to bottle.
The trademark symbols used on old soda bottles can sometimes be used to roughly date a bottle even if no other information is available. Many manufacturers have changed these symbols over time or were only involved in manufacturing bottles for a specific soda during a certain time range. For example, the Owens-Illinois glass company used an O inside a diamond on Coca-Cola bottles manufactured before the mid-1950s, but switched to an I inside a circle after that time.