I have found some examples already for copper, ie: https://www.youtube.com/watch?v=OTGZcY7WyYI but I am wondering if there is any other known tried and tested methods for using a laser to draw designs onto a resist coating over sterling silver or other metals for acid etching?
The only difference between etching silver and etching copper is that the silver takes longer to etch (in general) and it does not work with chloride based etch chemistry like what they are showing in that video.
If you use a nitrate based etch (i.e. Nitric acid or Ferric Nitrate) then the black spray paint should work well. I have etched sterling silver using spray paint and manually scratching through it with a scriber, and it works great.
The laser should be the same, just a lot faster. 
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This makes me so happy… I’m kind of amazed the spray paint survives the etching process, honestly. Does it have to be any particular kind of spray paint, or any kind of special process?
I used Krylon brand since I had it, so I know that works.
That said, I doubt there is that much difference between brands and you are best off just experimenting.
Some of the etchants may dissolve some paints but not others, or even some colors and not others depending upon the binders. Back in art school we used to paint on a thin layer of tar (!) as a resist, and it works really well since it is slightly flexible. I have no idea if it is laserable, but I intend to find out.
There are also “laser safe” frisket films that might work if you apply them carefully, and that might be good if you are trying to do a really deep etch (paint will tend to lift if it gets undercut at all).
If you want to etch brass, steel, even stainless, the standard Ferric Chloride circuit board etch will work pretty well,. Accelerating it with some Hydrogen Peroxide will help if you are impatient. 
There are lots of great online resources for etching, and really the only thing the Glowforge is adding is a fantastic way to cut through the resist.
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You can even use more substantial resists, right? Something like a piece of paper or plastic stuck to the face, let the laser cut that off, then into the acid? I seem to remember doing that for an art project once.
Yes, that would be the “frisket” I mentioned.
I think self adhesive mylar works, but you need to be careful to apply it without getting any bubbles.
You might be surprised at how well spray paint or wax/tar (also called “soft ground” to intaglio printers) works.
People have been using the process for a very long time.
Here are a few good links to learn more:
http://www.wretchedetcher.com/etching-tutorial/etching-apply-ground.html
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Thanks for all the great info!