This sign is simply a capital letter L, written in an old-fashioned handwriting style and 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.
