what Mark said. Each sign and each time will be different. Sometimes it will clean up great, other times it will clean up but leave a rust like shadow, other times it will clean up but completely remove all gloss.
One thing that is consistent is that most of the time it is an improvement... and it will require some work. Nothing will magically melt the rust away, some elbow grease and time will have to be put into it.
Yes I agree I had a sign that was cobalt blue and it took the gloss right off and ruined the sign. But I have used it several other times on other signs and it has worked great.
