Disable iBeacon settings
The quick answer is that iBeacons use bluetooth low energy, so simply turning off bluetooth will opt you out of tracking as well as notifications.

The longer answer is that iBeacons don't track you or your iPhone/iPad in the same manner that WiFi scanning and cell towers actually can track your devices. You choose which beacons to pay attention to.

Think of the difference between a red traffic light and a red light camera. The red light is a beacon that you could choose to track and pay attention to. The red light camera doesn't care whether you are paying it attention - you get captured if the device is recording. The license place on your vehicle is the same as your WiFi MAC address. It is trackable and traceable. Bluetooth low energy and iBeacons doesn't have any trackable item until you pair with a specific device so you are safer than with WiFi.

For this reason, most retailers have been tracking WiFi for years before iBeacon bluetooth were introduced. Even though bluetooth has the ability to work at shorter ranges and provide a more precise location, it has privacy built in to the way beacons are architected. You will want to disable WiFi and perhaps turn off your cell entirely if you want to have more meaningful privacy in store spaces where companies are monitoring traffic. With iOS 8, you can just forget all the WiFi networks you don't want to track and the device should be anonymizing your WiFi MAC address (the license plate) so that everyone has the same "mask" on until you actually join a specific named network.

In summary, to avoid seeing any iBeacon advertisements, don't install apps that will look for certain beacons and do things. If you do install those apps or passbook items, then disabling bluetooth will still opt you out of iBeacon activity on the device.