These are Price Headley's Acceleration Bands. They act as a trading envelope and a trend trading indicator and was first seen in 2002.
Basically, the indicator uses the concept of “acceleration” to get into and out of securities.

When price breaks the bands, it's a signal of a trend in that direction. So for example, if price breaks the upper bands you should be looking to buy at pullbacks.

Coded by Mladen some years ago, they're an interesting indicator to use.