The members of PrivacySIG have all agreed to always aggregate data and not to track individuals. Your unique MAC address will only be used as part of a count, as in "53 visitors visited Store X today".

If you do not want your device to be used in this way, you can opt-out here and your device will be not be used for future statistics.

Here are the steps for finding your MAC address on common devices. If you device is not in this list, please refer to the documentation for your device. 
 
Android
Settings > About phone > Status > Wi-Fi MAC address 
iOS
Settings > General > About > Wi-Fi Address
Symbian S60
Dial the number: *#62209526#
Symbian S40
WLAN > Available WLANs > Options > Details
Blackberry OS 4.5-5.0
Options > Status > WLAN MAC
Blackberry OS 6.0-7.1
Setup > Options > Device > Device and Status Information > WLAN MAC
Windows Phone
Settings > About > More info
Sailfish OS
Settings > System > About product