While searching on the USPTO site you must be aware that it's not 100% accurate. As the process takes quite a bit of time. Therefore, something might be in the process of being trademarked and will not be listed. In order to get a 100% accurate search you may need to hire somebody to do it for you. However, it is much more expensive. Generally around $200. Depending on your situation it can be worth it to just risk it and apply rather than wasting the $200 on the search fees. Obviously two professional searches and you've got yourself another trademark and some change.
Good luck!