In the image, a T is drawn in a C. If you pronounce this, you will say tea in sea. So the image refers to the Boston Tea Party (Boston, December 16, 1773). During that event the colonists were angry at the English government because of tax measures. Some of them destroyed ships which were filled with tea, a large part of this tea was dropped into sea. The Boston Tea Party was one of the events which eventually led to the American revolutionary war. (See also Wikipedia: Boston Tea Party)