As I looked this up, it seems that this is the question of many authors: What do you do about words that may be trademarked or words that may be accidentally advertising something?
I did not even realize this could be a problem. I sent the rough rough rough rough draft of chapter 2 of my book to a friend I talk with over MSN. She pointed out my use of specific vehicles within the text. For example: 'Ford Explorer' or 'Toyota 4Runner.'
At first, she said I should change these to SUV or truck or car, etc., but by the end of the chapter she realized it was important to the story to keep the specific makes and models. At that point, we were both stumped as to how to proceed.
I tried looking it up and found words like 'Kleenex' should be 'tissue' while writing and stuff like that, but I didn't find anything pertaining to something like a vehicle make and model. One site I ran across seemed to think it was okay to use a title like that, as long as it is kept true to form of the trademark. For example: 'Ford 4Runner' could never be used, because Ford doesn't make the 4Runner, Toyota does. So, according to that site, it would be okay to use 'Ford Explorer' as long as it's a Ford Explorer in the book and not something make believe that isn't a Ford Explorer while calling it a Ford Explorer.
After reading through all that, I realized I was on someone's blog. So, it wasn't a fact but an opinion that it was okay to use words/titles like that.
My own opinion on the matter would be that it should be okay, since it is kind of like free advertising. However, I also understand how someone could get upset if their trademark was used in a way they wouldn't want it to be represented. It's turning into a difficult question, one I don't have the answer for.
I also remember reading a bunch of stuff that Amanda Hocking uses and doesn't seem to worry...such as the words 'Jim Henson's Muppets' or specific movie titles within the text, etc.
I'm moving forward as if it's okay to use a specific vehicle type, but does anyone know more about what the rules are on this kind of thing?