!

Exclamation mark in: Tristram Shandys levned og meninger 1st. danish ed. (Borgen, 1976). Copy at the Main Library in Århus. 

Exclamation mark [!] [eks.kləˈmeɪ.ʃənˌmɑːk]:

The modern graphical representation of the exclamation mark is believed to have been born in the Middle Ages. The Medieval copyists used to write at the end of a sentence the Latin word io to indicate joy. The word io meant hurray. Along time, the i moved above the o, and the o became smaller, becoming a point.

The exclamation mark was first introduced into English printing in the 15th century to show emphasis, and was called the "sign of admiration or exclamation" or the "note of admiration" until the mid-17th century; admiration referred to its Latin sense of wonderment.

The exclamation mark did not have its own dedicated key on standard manual typewriters before the 1970s. Instead, one typed a period, backspaced, and typed an apostrophe. 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.