The hydraulic system is functionally similar to the B206 system for example, which also does not have a light or a gauge (similar to many light single engine helicopters that use hydraulic power-assistance controls, as distinct from hydraulic power control). The hydraulic system is powered from a pump mechanically driven from the MGB transmission and is controlled electrically, because it is not practical to route the hydraulic system direct to the cockpit. The electrical control system is "fail safe" in that if anything shuts off the wigglies to the valve that dumps the hydraulic pressure, it fails so that hydraulic pressure remains ON.
When a helicopter has only one hydraulic system, failure of that single system is foreseeable and it must be possible to cope with such a failure in flight. That's why the aircraft can be flown without hydraulics and we practice hydraulic failures in types that have such single systems. If not, you would need at least 2 entirely redundant systems.
The light or gauge would not really help you much - you notice almost immediately if you lose hydraulics in flight!