All comes down to usage. Having multiple trademarked acronyms in different verticals can actually make a domain more of a liability - even harder to run any kind of adsense on it without infringing, and almost impossible to park.
In theory, you could own ABC.com and run a site helping kids learn the alphabet and you'd should be fine, but ABC have more money and lawyers than you, theory doesn't always hold.
Look at the mess Apple got into with the Beatle's music label (also called Apple). Who would have ever predicted 20 years ago that the company would become the largest digital music seller on the yet-to-be-public internet?