We have had questions from local companies wanting to sponsor our robotics team and we were wondering if we could have company decals on our robot? Similar to nascar.
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Hi! We have not tried decals, but if the answer turns out to be no, one thing my team (STEM School in Colorado) does is offer to laser-engrave the logo onto a robot part. One year they laser-engraved all the sponsor names and logos onto a scrap kit wood plaque that they velcro'd onto the side of the robot. It's another way to go about it without having to worry about compliance.
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I have seen sponsor logos on robots in past years, so I think sponsor names and logos (in good taste) would be fine, as long as you dont use them for a "functional" purpose, such as interacting with the game field or pieces. 

IGUS is a major BEST Sponsor (by providing that bag of plastic bearings and rods, etc for every team).
They include an IGUS logo sponsor sticker in the bag, and I have seen teams use that.

Or, you know, questions like "is it allowed to X?" could always be asked on the Q&A.
That way, you'll have an official documented answer to show judges that question you about it.
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