The New York American League baseball club is generally known to baseball historians as the "Highlanders" for its 1903-1912 era and as the "Yankees" starting in 1913.
Both nicknames, "Highlanders" and "Yankees" were used before 1913. Initially they were simply known as the "Greater New York Baseball Club" when they came to NYC in a deal that allowed the Baltimore club to move.
To NY Giants fans, they were the "Invaders", a name that actually appeared in newspapers like the New York Evening Journal in 1903.
The new team built its new ballpark on a high point of Manhattan called "The Hilltop" and "Hilltop Park" became the name for the American League Park. The press dubbed the team the "Highlanders" and the name stuck though it was never "officially" adopted by the team itself.
Those 1903 uniforms had only a large block "NY" which eventually evolved into the current NY logo of the Yankees.
The nickname "Yankees" first seems to appear in print in 1904. Though many people believe the Yankees name refers to their northern roots (as in Yanks versus Rebels), the term "Yankee" or "Yank" is a nickname synonymous with "Americans."
In a period when team names were not as formalized as today, many cities that had two baseball teams (Boston, for example) would refer to them as the "Nationals" or "Americans." to distinguish them.
The term was used popularly then including in a Broadway musical, Little Johnny Jones which featured the hit "Yankee Doodle Dandy."
Still, it was not a fixed name. In 1905, The Sporting Life referred to the team as the "Americans" and the "Highlanders" in the same article. But the nickname "Yankees" began to be used more and more often, and in a story by The New York Times about Cy Young's no-hitter of June 30, 1908, the team is called "Yankees" or "Yanks" and the ballpark is called "the American League Park."
The New York Times wrote about opening day 1912 that "The Yankees presented a natty appearance in their new uniforms of white with black pin stripes."In 1913, the American Leaguers left their Hilltop park and entered into a decade-long sub-lease with the Giants at the Polo Grounds which caused any reference to the "Highlanders" to be illogical.
It is not exactly clear what year the team officially began referring to themselves by the name. When Babe Ruth arrival in 1920, the "Yankees" was an established nickname did not appear on the uniforms.
Actually, YANKEES only showed up on road uniforms in 1927-1930, but in subsequent seasons NEW YORK was restored to the road uniforms.
The Yankees have also been unofficially nicknamed the "Pinstripers" (for their uniform) and the "Bronx Bombers", a reference to years of power hitters that dates back to the Ruth era.
Sources include:
http://newyork.yankees.mlb.com
The Complete Book of Baseball: A New York Times Scrapbook History
The New York Yankee Encyclopedia
New York Yankees Baseball Book
The New York Yankees Illustrated History
New York Yankees and the Meaning of Life
Dynasty: The New York Yankees, 1949-1964
For the Love of the New York Yankees
Dawn of a Dynasty: The Incredible and Improbable Story of the 1947 New York Yankees
For young Yankee fans in Training
New York Yankees 101 (101 My First Team-Board-Books)
New York Yankees ABC - My first alphabet book
