The exclamation mark, !, or exclamation point, is a punctuation mark usually used after an interjection or exclamation to indicate strong feelings or to show emphasis. In the 1950s, secretarial dictation and typesetting manuals in America referred to the mark as "bang", perhaps from comic books – where the ! appeared in dialogue balloons to represent a gun being fired – although the nickname probably emerged from letterpress printing.

Source: Wikipedia