A mark is a legally-registered word, phrase, symbol, or design that identifies and distinguishes a product (trademark) or service (service mark). The owner of the mark may exclude others from the use of words, phrases, symbols, or designs that create the same "commercial impression" in the consuming public's mind.
If you are working with trademarks for the first time, start with an overview of trademarks and the trademarking process, like the USPTO's "Trademark Basics" or one of the books listed in this guide.
Trademark Basics
Essential information from the USPTO about trademarks and the trademarking process.
A robust mark search requires multiple searches:
(a) Search the USPTO's Trademark Search database for registered federal marks and pending applications.*
(b) Search state trademark databases: Vermont trademark register. (Vermont does not register service marks.)
(c) Search the web, business name databases, and other publications for possible "common law" marks.
Trademark: Legal Care for your Business & Product Name by 
Patent, Copyright and Trademark: An Intellectual Property Desk Reference by 
Content Rights for Creative Professionals by 