An interesting question. Reminds me to much of the college essay I'm in the process of writing though, "What does it mean to be a member of a community?" Ugh. Anywho, enough of my complaining.
In short, I think it means that you have joined a unique "fraternity," in which you have to uphold certain things like professionalism, so as not give others a negative impression of aviation.
It also depends on how you define a pilot (one holding a license, one paid to fly an aircraft, etc.). I've only scratched the sufrace, however, so take it for what it's worth.