This symbol was created by Satoshi Nakamoto for the icon of an early version of the original Bitcoin client, though the very first versions of the Bitcoin client used "BC" instead of any special symbol. Presumably the symbol was intended to look similar to other currency symbols. The symbol represents the currency unit "bitcoin" (100 million satoshi), as well as the Bitcoin network and currency itself.
The Bitcoin sign was accepted for Unicode in November 2015 with the code point U+20BF (₿). The proposal was first submitted by Sander van Galoven from Netherlands and than by technology blogger Ken Shirriff, but it was on hold until Unicode version 10.0 was released yesterday by consortium members, adding 8,518 new characters including the bitcoin "₿" symbol.