Marriott fined $600,000 by FCC for interfering with customer WiFi hotspots
Marriott (since 2012) has been using wireless technology to prevent guests at the Gaylord Opryland hotel and convention center from using their own Wi-Fi mobile hotspots, forcing exhibitors or customers to use Marriott's expensive Internet services, available at the whopping cost of $250 to $1,000 per wireless access point. Despite popular press reports, this did not involve "jamming" which is strictly illegal in the US, but instead something more like a WiFi DoS attack.
Marriott had deployed a Wi-Fi monitoring system with a "containment capability". When activated, the system could identify Wi-Fi access points that were not part of Marriott's own Wi-Fi system (or otherwise authorized by Marriott). Such non-Marriott access points were dubbed "rogues". When rogues were detected, the system sent "de-authorization" packets to the unauthorized access points, booting those users off their free connections and, presumably, forcing them to pony up for Marriott's paid Internet access.
http://www.commlawblog.com/2014/10/articles/enforcement-activities-fines-f/marriott-whacked-for-600000-for-war-on-rogue-wifi-hotspots/
Marriott had deployed a Wi-Fi monitoring system with a "containment capability". When activated, the system could identify Wi-Fi access points that were not part of Marriott's own Wi-Fi system (or otherwise authorized by Marriott). Such non-Marriott access points were dubbed "rogues". When rogues were detected, the system sent "de-authorization" packets to the unauthorized access points, booting those users off their free connections and, presumably, forcing them to pony up for Marriott's paid Internet access.
http://www.commlawblog.com/2014/10/articles/enforcement-activities-fines-f/marriott-whacked-for-600000-for-war-on-rogue-wifi-hotspots/
http://www.fcc.gov/guides/over-air-reception-devices-rule
You'd need a lawyer specializing in this stuff to determine if they've made any rules that might apply to restrictions on the use of WiFi. It's extremely easy to locate a WiFi hotspot. Android devices have WiFi Analyzer which will beep like a signal meter as you approach a given AP. Then just walking around the location, you'll be able to use that info to narrow it down to a 20ft area, or so. You can do the same with any WiFi device that displays the signal strength of individual APs, just needing to watch the numbers, or otherwise write your own program to beep and show a relative gauge.
It would be much faster, easier and more accurate still, if coupled with a directional WiFi antenna connected to your device, to narrow it down to exactly which person at a table has the AP in their pocket.