14 is likely a date code for 1914.
From my site:
Hamilton, James T & Albert, (1879-1943),
Pittsburgh, PA, United States, Occurs on 2 bottle,
Manufactured beer bottles. James T. and Albert were associated with the W. H. Hamilton glass works until 1879, when they established their own glass works at 26th and Railroad Streets. Their specialty was flint glass bottles, which included beer, whiskey, and milk bottles in addition to prescription wares. In 1887 a plant was established at Butler and in 1902 a third plant was opened at Blairsville. Albert was murdered in 1902 and James continued the works incorporating on December 11, 1916. The milk bottle business was to be sold to Thatcher in 1920, but Hamilton was advertising machine made milk bottles in 1922 and in later years before the business was sold to Knox in 1943. At this time the factory was renamed the Seaboard Glass Bottle Co. The makers mark was filed in 1912 and was issued a trade Marked in 1915. The application claimed it to be in use in 1900. The markings are on the base of the bottle.