The exclamation mark, also sometimes referred to as the exclamation point in American English, is a punctuation mark usually used after an interjection or exclamation to indicate strong feelings or high volume (shouting), or to show emphasis, and often marks the end of a sentence, for example: Watch out! Similarly, a bare exclamation mark (with nothing before or after) is often used in warning signs.
This is a companion discussion topic for the original entry at http://grammarerror.com/tags/exclamation-mark