SINGAPORE -- While Tesla's $1.5 billion investment in bitcoin has added to recent excitement over cryptocurrencies, the blockchain technology that underlies their use is creating another opportunity in capital markets -- which Singapore is doing its best to capture. The city-state, one of Asia's bigger financial centers, is emerging as a trading hub for digital securities, or security tokens backed by financial assets. Exchanges to trade these innovative securities are being set up by both local and external players, which hope to attract issuers and investors to their platforms.