Wouldn't it be useful if D and DS modes displayed the current "gear"? e.g. D1, D2, D3 ... D6
Or is there already some way to see this that I am missing?
How do you guys know for sure if your cars are starting in first or second in D?

 

I agree. You just have to get used to how the various gears feel and, perhaps, count shifts. Also, you could always start in DS so you'd be sure you start in first and then move the lever to the right to get to D when ready. When starting in D, you just have to sort of trust your car to be starting in the gear you expect. In this regard, having to trust your car is not much of an issue unless you want to accelerate rapidly. And, if you do, then the car should start in first whether in D or DS if floored. You might end up being in second when wanting to be in first, however if you want to accelerate rapidly without flooring the car.