There are millions of businesses with registered trademarks and many produce numerous products and services. Unless it is a totally fanciful mark (a “made-up” symbol, like the Nike® “swoosh”), it is doubtful that your selected mark will be completely exclusive and not in use, in at least some similar fashion, by someone. The main question is how similar your mark can be to another mark and still avoid infringement? You may get away with using a similar mark to an already registered mark for several years, but when the owner notices you, it may be very expensive to make a change.