You should see an audio player above. Listen and you'll hear an auditory illusion. (I don't recommend listening for the full 5 minutes as this may cause temporary insanity…)
This illusion is analogous to a well-known visual illusion which you are likely to encounter outside what kind of business?
Hint
If that auditory illusion was a little too spooky for you, here's a palate cleanser:
Wikipedia has more on the barberpole illusion and the strange history of the barber's pole. Choice quote:
Enjoy these two performances—the source of yesterday's hint, plus a piano piece loosely based on the Shepard scale.
Solution
Sounds like an endlessly rising tone, right? This illusion is called a Shepard scale. It's a smooth version of playing all the C's on a piano, then all the D's, then all the E's, and so on. Eventually you're back to all C's; it sounds like you've gone up an octave, but you're really exactly where you started.
It's just like… a barbershop pole!
In Renaissance-era Amsterdam, the surgeons used the colored stripes to indicate that they were prepared to bleed their patients (red), set bones or pull teeth (white), or give a shave if nothing more urgent was needed (blue).
Honorable mention to Jacob for thinking of Penrose stairs (see right); alas, they are not commonly displayed outside any kind of business that I know of.
Congratulations to yesterday's solvers Peter M., Dr. Yetman, and Mr. Gregg. Thanks to everybody who made a guess!