This paper argues that the mapping between identifiers and end-investors should be a market design choice. It captures features of blockchain technology in a theoretical model of intermediated and peer-to-peer trading, and studies the impact of the usage of identifiers and the corresponding transparency of holdings on trading behavior, trading costs and investor welfare. Despite the risk of front-running, the most transparent setting yields the highest investor welfare. In the absence of full transparency, for low levels of liquidity in the intermediated market, welfare is highest if investors are required to concentrate their holdings under single identifiers.