What meaning does the Starbucks logo have?

There is a long, involved history of how the logo was developed. Be sure to read the story of how the Starbucks siren became less naughty, here:

http://www.deadprogrammer.com/starbucks-logo-mermaid

The wikipedia article will tell you briefly about how the mermaid lost her tail and her navel and chest were "cleaned up" because of an embarrassed elementary school principal. http://en.wikipedia.org/wiki/Starbucks