You really need to pull the wheels, one at a time, and check for overly worn pads / shoes. As your brakes wear, the fluid level naturally goes down. While the system might be leaking, it could also be that you are very low on pads / shoes. For the fluid to get that low without a leak, you would likely need to be very low on all four wheels.

You may wish to consider getting a positive pressure one man bleeding kit. You fill the devices reservoir with brake fluid, then pressurize it. It's outlet it screws on to the top of the brake fluid reservoir. You can then go around to each wheel in the proper order and flush a good amount through each of the lines, then turn off the bleeder valve at that wheel. This gives you fresh fluid in the system but also should help you detect leaks because of the constant pressure from the device holding the fluid. If it is leaking somewhere, it will leak faster under pressure in most cases. You'll just need to find the right adapter top for the Saturn brake fluid reservoir.

I recommend doing this with all four corners supported by Jack stands with all four wheels removed. This gives you easy access to the bleed valves. If you are nervous about stability, break the lug nuts loose while the car is on the ground as usual, put it on jack stands, and only take off the wheel that you are working on. That we should give you a catastrophic failure you still have three wheels on their lugs at any given time.

Being a 1992, there is the real possibility that one or more of the brake lines, the metal brake lights, are starting to rust through. If this is the case, you may not see direct dripping the fluid. The fluid may cling to the outside of the metal brake lines and run for some distance based on the shape of the line. Use a bright light when you're down there to look for the wetness and ensure to assess the state of health of the metal brake lines.

Thanks for all the detailed suggestions, derf. Unfortunately, I'm an old StarLady, so there's no way I can be getting "down there." :o My mobility range is pretty limited, so I can only do easy stuff that doesn't require stooping down or getting on the ground. I would need a mechanic to do any work like that.
But I'm sure your suggestions will help the next person who looks at this thread looking for help.

If you have a trusted shop that you use for various things, take it to them and ask them to put it on the lift and look for any leaks on the brake lines. If they "spot one or two" ask them to show them to you. If they tell you that they can't let you into the shop because of safety issues, hand them your phone and ask them to take photos for you. An honest shop will be willing to do that. If they refuse, you need to find another shop.

Please do not ignore the state of your brake system in this vehicle. At best, the system runs dry and you hit the brake pedal and, well, nothing happens. Nobody wants that.
If it's a leak, it leads to the same end result. No brakes.
If one of the lines ruptures, the remaining fluid in that line will drain all at once and your braking will be impaired.

It is critical that you get this addressed.

Success! Yes, adding fluid did the trick. I went driving, and the brake warning light went off after starting the car. And stayed off. Tested engaging the emergency brake a couple of times, and the warning light came on and went off as it should. All is well now.

Thanks, everyone, for all your great advice. I doubt there's a leak, and I think the fluid probably went low because the brake pads need replacing. I don't even remember the last time that was done, and haven't thought about it because I've had no issues with my brakes. But maybe i've just gotten used to the brakes being 'softer.'

Anyway, I'll be sure to get the underside inspected the next time my car sees a mechanic. Which will probably be in the next couple of weeks -- my baby needs an oil change badly (among many other things).

Thanks again! :)