Beside imitating psst sound, you can also imitate loud engine rev noise when accelerating.
You probably have heard some cars with very loud engine noise. Some are real turbo engine noise and what about the fakes? Poseurs fix a whistler inside their muffler to generate turbo noise. The loud engine noise come from the whistler inside the muffler and not from the engine.
Check out this site
http://www.turbowhistler.com/ for details on turbo whistler.
Together with the psst sound simulator as mentioned earlier, you can get an 'embrassing' turbo car.

Another product strictly for poseurs only.