Trademark, if you are an affiliate of a merchant who has a brand name, and you use it "fairly" to point to thier website. There is no problem, its fair use. However if the affiliate agreement states otherwise, consider this and make your decision. Search engines tend to be a no no. I personally agree with it, I have a company that has used my company name, my company mailing address just so they can sell mortgages, after the holidays Ill deal with them. I like the categorizing of merchants, it serves several purposes, easy for the reader, visitor or shopper to find stuff, two and most importantly, easy for you to find should you have to remove the affiliation for one of a thousand reasons it seems lately in affiliate marketing. If you really need more information about trademarks and other information of this type, I regularly head to
www.firstgov.com, every state of the union is here, federal goings on etc, and they have really made it very easy to find stuff.