Without any legal basis for my comment, my thoughts would be that if you were somehow portraying their products in a derogatory fashion AND your work became popular enough to get them to notice you, then you might have a problem.
OTOH, FedEx made a small, independent coffee bar called, 'Federal Expresso' change their name...
Well, I suppose I could always plead ignorance.....at least the stuff I shoot isn't derogatory.