I picked up a 5" post vise a couple of weeks ago and started wire brushing and waxing it. So far I have only found a couple of numbers (Sorry, I didn't get a picture of them yet).

Are there other distinguishing features that give a clue to it's origin or age?

 

The shape of the box, the smallish ears at the jaw bases, and the overall shape tell me that it's a Columbian.

Probably an older Columbian by the shape of the legs and the screwbox 

This is my first post vise, if it is, in fact, a Colombian, is that a good one?

When you say older, what are you thinking? I don’t know the history of that company.

The parts all seem to be in excellent condition. The screw was coated in petrified grease, but shows no damage or much wear after cleaning. Same with the screw box.

Although  It looked like it was buried in a field when I got it, The whole thing is cleaning up rather nicely. 

I have five columbians and one Peter wright and a couple of Frankensteined vises they all work just as good any other , if the jaws and screw- screwbox are in good shape they are all about the same , in my opinion. I'm sure I'll be proved wrong .

Many post vise you would not find out the identity. Since many are unmarked. From what I've learned and experienced, if the screw and screw box is good then it's a good servicable vise. The rest is pretty easy to make or repair. 

The only "bad" postvise is one damaged or worn past use.

Good answers! Thanks all