Fire ratings depend on the material the label is going to be put on. Putting a heat rated material on plastic, wood, and other materials that will melt or combust won't really do much good. And usually the person asking has a response like, "Oh, I didn't think about that." I have been tasked to research this a few times.
We sell material that will go through solder baths, on the inside of grills, on tail pipes, etc. If a customer wants something on a tail pipe, it might have to last up to 400°-500°F. But if they want it on a header, the temp is a lot higher, and now you're talking big bucks for the media, and you can't buy a 10 yd. roll. Thermal Resin colors will last through really high temperatures, but solvent inks won't... or so I'm told by some in-mold decorating guys I know. Grill Covers get really hot, and can be hot for long periods of time. But there are labels that will withstand those temps, so it might be good to get more specific details about how hot it will get, and what is the sign/label going to be applied to. Like the steel/porcelain combo, when they see the price, they'll probably drop the idea.
Doug Goodloe
Graphic Marking Systems
800-232-8018