Where did the pound sterling symbol originate?

The official full name pound sterling (plural: pounds sterling) is used mainly in formal language and also to distinguish the currency used within the United Kingdom from others that have the same name. (GBP = Great British Pound)

As a unit of currency, the term pound originates from the value of one 'tower pound' (326 grams) of high purity silver known as sterling silver. Sterling silver is an alloy of silver containing 92.5% pure silver and 7.5% other metals, usually copper. The Word sterling is believed to come from the Old Norman French esterlin (meaning little star) transformed in stiere in Old English (strong, firm, immovable).

The currency sign is the pound sign, originally ₤ with two cross-bars, then later more commonly £ with a single cross-bar. The pound sign derives from the '£sd' pronounced, and sometimes written as 'LSD'. The abbreviation comes from librae, solidi, denarii (libra was the basic Roman unit of weight; the solidus and denarius were Roman coins). '£sd' was the popular name for the pre-decimal currencies pounds, shillings, pence of Britain and other countries.