When is it fair use to use a company's trademark?
Apple, IBM, Exxon, Facebook. There, I wrote these trademarks in my article, but I didn't get permission first. Am I getting in trouble?
Trademarks uniquely identify a source of a product or service. Use of a trademark is using the name, logo, slogan or other unique identifying symbol of the source, in association with those goods and services. It must be in a way that is confusing (and famous marks have a larger ambit of protection.)
So if you sold a smartphone or computer, and called it Apple, then you would be using Apple's trademark and would leave yourself open to a trademark infringement law suit. However, if you sold a fireplace insert, and labelled it with the mark APPLE, you would not be "using" Apple's trademark (until Apple develops fireplace inserts!)
Most of this is common sense, but, in general terms, a trademark does not prevent anyone from using that word, logo, slogan ever again, rather it restricts the use for the sale or advertising of the products related to the brand.
Further, there are clear exceptions on trademark use for fair comment, like journalism or parody, and also these are not "uses" of the mark.