The hashtag's real typographic name? 'Octothorpe.'

The word "hashtag" is a neologism for the # symbol, sometimes called the pound symbol in American English (but separate from the British Pound symbol, £ ). More properly called an octothorpe, the # is anything but new; and actually dates to the Roman Empire.

The "@" symbol, now commonly called "at," was originally used to take the place of any word beginning with "a."

☛ The little pointing-hand symbol, used in some typographic lists, is properly called a manicule, and is sometimes referred to as an index or fist.

If this kind of lexico- and typographic trivia interests you, you'll enjoy the "Shady Character" blog.

http://www.shadycharacters.co.uk/