According to a post on the Radar Relay Medium, Short Ether or sETH, the first short token, is now available for trading on Radar Relay. sETH is a short position in Ethereum abstracted in an Ethereum token built on the dYdX protocol. Trading short tokens on Radar Relay is the same as trading any other ERC20 token on the relayer.
This is a significant breakthrough for cryptoassets and decentralized trading, as traders and algorithms can now hedge portfolio risk and take short positions via tokens. Tokenized short positions can serve as both a risk management tool to combat bearish price action or a hedge on a substantial position.