People look for these for all kinds of reasons, such as whether a security system is armed or not. Some people end up making their own.
There are discussions of a number of different devices that people have used for status indicators in the following thread. (The topic title is a clickable link.)
However, all of those have the same limitation: they are going to turn on when you press the button whether the circulating pump actually comes on or not.
If you need to know if the pump actually turned on, you have to look for something measurable there. Does the pump itself have an indicator light? Does it vibrate or get hot? Is it plugged in so you could measure the electricity it is drawing? We’re just looking for something that would change physically when the pump starts so that you could get a report on that. That way you would know for sure that the pump had started rather than just knowing that the request had been sent.