For coin perpetuals, which are settled in the underlying cryptocurrency, the contract ticker will end with "-PERP". For example, the ticker for Interdax's bitcoin perpetual contract is "BTC-PERP". The contract tracks the BTC-USD rate and BTC is used as collateral. The ether perpetual contract, the ticker is "ETH-PERP", is settled and margined with ETH.
For stablecoin pereptuals (or USDT perpetuals), which are contracts settled with USD Tether (USDT), the contract tickers will end with "-PERP-USDT". For example, the ticker for Interdax's LINK perpetual contract is "LINK-PERP-USDT". This contract tracks the LINK-USD rate and is settled and margined with USDT.
Tickers for spot trading instruments end with "_USDT". For example, BTC_USDT is the spot trading instrument for bitcoin against USDT and ETH_USDT is the spot trading instruments for ether against USDT. Spot trades will not create a position in the positions panel, since it represents an immediately settled exchange of one balance with another, i.e. exchanging BTC for USDT or vice versa.