The symbol was encoded in Unicode version 10. Currency Symbols block in June 2017. Without proper rendering support, you bitcoin server hardware see question marks, boxes, or other symbols.
It is the first decentralized digital currency, as the system works without a central bank or single administrator. The system works as a peer-to-peer network, in which transactions take place between users directly, without an intermediary. These transactions are verified by network nodes through cryptography and recorded in a public distributed ledger called a blockchain. Bitcoins are created as a reward for a process known as mining.