To get us started, we should talk about logos, trademarks, and what constitutes a brand. Two branding guys at The Blake Project give us a short definition of the visual parts of the brand and a very good description of what is meant by “brand value”:

A logo (trademark and its associated visual language) is the symbolic representation of a whole narrative story built into an organization over time. Brand equity is the result of successfully delivering on the promise your brand represents in the hearts and minds of consumers.

So the trademark is the most basic representation of your brand. The logo and identity (visual brand) includes the trademark along with how it will be presented - for example, color schemes, position and page architecture - and the brand is the associations, particularly the emotional associations, people perceive when they see your logo. So the logo, to successfully represent your brand, should help to convey the emotional associations you wish your brand to impart to both existing customers and potential customers alike. And, to make sure those emotions are associated with your brand and your brand alone, it must be unique in the marketplace.

http://www.brandingstrategyinsider.com/2011/01/branding-debate-does-logo-design-really-matter.html