This sign is simply a capital letter L written in old-fashioned round hand with one or two crossbars to show that it is being used as a symbol or abbreviation. The L stands for the Latin word libra the name of a Roman unit of weight which also gave rise to the abbreviation lb for a pound as a measure of weight and to the French word livre. The symbol for the Japanese yen was probably invented by analogy with the pound and dollar symbols as it is a capital Y with one or two bars across it.
