USDT.D represent the dominance of USDT in the crypto market. If it goes up meaning crypto coins are down and many hold USDT. However, that does not mean you can use it after-effect! it only helps you to see where the market is going as now USDT.D Setting on a strong resistance level therefore it should go down. As a result Alts and Bitcoin will go up.
Furthermore: Here in the chart, I set alarming levels. You can also set the alert levels as Warning to take-profit. These zones usually the market test them and bounce up.