Redsand... I was having the same problem, with no solution for months (mind you, I hadn't asked the experts here). The difference in my problem is that I was to use graphics (red octagon, yellow triangle, green circle). I had the jpg's, but was not sure how to implement. It came to me last week that I could put the 3 graphics in place, on top of each other, and use conditional supression of the graphic based upon a formula. The graphics will look sharper than webdings, etc., so if that would work for you it might be a solution.
Hope that makes sense... I think it is easier than the solution you're working toward.
If that won't work I believe (with v10 at least) you can use html in your formula which should allow you to conditionally set the font. I have only tried that once, and I don't have CR on this computer, so I'll have to defer on the specifics. I was reading details in the help file earlier this week, but had to stop for a different project.