Hold the command key and drag it off the menu bar. It will be gone in a puff of smoke.
Is it there during bootup?
If so, try going to system preference->account->login items and see which apps are designated to run during startup.
Also look in your Application folder and check if an app with the same icon can be found there.
Open system preferences and under accounts select yourself and look to see what you have in the login items. It's no doubt there.
Maybe check the utilities folder for the same icon...?
What is that S with the face icon all the way on the left