When Didi kuaiche does a subsidy for a taxi ride (never use zhuanche, which is non-taxi), they send a message to your phone telling you that they added a bonus to help you get a taxi. It is usually 5 kuai, which is just less than a dollar.

My wife uses zhuanche, and they don't necessarily subsidize rides, but they give riders coupons to "try" the service (say 15 kuai or so). It is a bit more expensive than a taxi, so in a way this is a subsidy also.

Have no idea about Uber specifically.