Kilz comes in a spray-upward can: read the labels carefully. It smells to high heaven but will seal out the ordinary watermark. It is dead white, so you may have to repaint the ceiling afterward, but it will stop the brown stain.
If you should get mold, there are some other spray-ons that will remove the mold right before your eyes: x-14 is one of these products: it's a good version of watered-down chlorine bleach, so don't get it on your clothes. I bought a fixer-upper with a compromised roof tree, leaks, and mold...I got a real education in fixing these problems.
If you have a popcorned ceiling, there is also a product you can mix into the ceiling paint to sort-of replicate the look of the rest of the ceiling, but this is iffy: if it's too bad, you just call a guy who blows ceilings and have him do a patch to blend in with the rest.
Glitter? There's even a machine to put that stuff back on. It's messy beyond belief, and you sparkle in the sun after using it---for weeks.