The bike I've purposed as the winter beater was mostly the right machine for the job, and was certainly the right price on Craiglist.

But it looks as though the fork originally had v-brake bosses, and the previous owner removed them. At any rate, it now has two circular patches of unpainted steel on the fork.

Any suggestions an appropriate coating to prevent these from rusting in salt and snow?

I asked my bike manufacturer for touch up paint and they recommended automotive touch up paint that you buy in auto parts stores.

I've used nail polish for deep scratches. ...uh, my wife's nail polish.

Take it to your local Walgreens or wherever and buy some fingernail polish. You can probably find a pretty close match. If you aren't too picky you can just get whatever is cheap and kinda close. I just used this techinque on my commuter which had some big chips in the paint and lots of small ones and it looks so much nicer I am tempted not to call it a beater anymore. =) Before applying the paint I just wiped it down with rubbing alcohol.

I've also used nail polish with success. Finding the right shade (or one close enough) is tricky. I took a digital picture, went to Walmart and bought quite a few just to try each one. I simply returned the ones that didn't work. They don't like it when you try'em at the store.

Stole some of my daughters nail polish ,it works well as touch up paint.

I use automotive touch up paint.

theres small vials of paint in my big box store..

I've used model enamel to good effect. Take your time and blend colors to get a good match.

try some plain old Rustoleum ?
it is made for the purpose.
smooth the exposed spots with some steel wool or a wire brush,
wipe the filings off and with a small brush - neatly cover the area.
depending upon the original color, red base rustoleum contrasts nicely with
many colors or match the paint color - there are a lot of choices.