echnically speaking, a trademark is any word, design, slogan, sound, or symbol (including nonfunctional unique packaging) that serves to identify a specific product brand -- for instance, Xerox (a name for a brand of photocopiers), Just Do It (a slogan for a brand of sport shoes and sportswear), Apple's rainbow apple with a bite missing (a symbol for a brand of computers), the name Coca-Cola in red cursive lettering (a logo for a brand of soft drink).
A service mark is any word, phrase, design, or symbol that operates to identify a specific brand of service -- for instance, McDonald's (a name for a brand of fast food service), Kinko's (a name for a brand of photocopying service), ACLU (a name for a brand of legal organization), Blockbuster (a name for a brand of video rental service), the U.S. Postal Service's eagle in profile (a symbol for a brand of package-delivery service), CBS's stylized eye in a circle (a symbol for a brand of television network service), the Olympic Games' multicolored interlocking circles (a symbol for a brand of international sporting event).
In addition to trademarks and service marks, federal trademark law protects two other types of marks -- certification marks and collective marks.