According to the Star Trek Sticker Book (Pg. 9), by Michael Okuda, "At one time, it was thought that the three bright stars in the starfield might represent Earth, Vulcan, and the Klingon Homeworld, since during early episodes of Star Trek: The Next Generation it was thought that the Klingons might have actually joined the Federation. When later episodes made it clear they had not, the three bright stars were left undefined."
What about Tellar. Aren't they founders of the Fed as well?
They are, however the catalyst for the formation of the Federation was the Humans stopping the bickering between the Vulcans, and the Andorians. Later they stoped the bickering between the Andorians and the Telerites.