This may be 2010 emails just now being released on a program in effect then that may or may not be in effect now.
Devlin Barrett, "Gun-Show Customers’ License Plates Come Under Scrutiny", Wall Street Journal, 2 Oct 2016.
http://www.wsj.com/articles/gun-show-customers-license-plates-come-under-scrutiny-1475451302
Federal agents have persuaded police officers to scan license plates to gather information about gun-show customers, government emails show, raising questions about how officials monitor constitutionally protected activity.
Emails reviewed by The Wall Street Journal show agents with the Immigration and Customs Enforcement agency crafted a plan in 2010 to use license-plate readers—devices that record the plate numbers of all passing...
Yep, you do need to be subscriber for the full story.
Wall Street Journal interviewed attorney Jay Stanley of the American Civil Liberties Union who said the program was troubling.
Chris White, "Emails Show Federal Agents Used License Plate Scanners to Collect Information at Gun Shows", Law Newz, 3 Oct 2016.
http://lawnewz.com/high-profile/ema...scanners-to-collect-information-at-gun-shows/
... According to the report, agents justified the operation by saying they compared data collected at the gun shows with information obtained from license plate scanners at border crossings in the hopes of finding gun smugglers. However, the report found no evidence that “the gun-show surveillance led to any arrests or investigative leads.” Yet, the newspaper says there are indications that the gun show surveillance may have been used at other gun shows throughout the state, and possibly the country — despite the apparent lack of arrests. ...
Surveillance of gun show attendees then or now is stuck on 40% stupid. Check the percentage of criminals who obtain guns from gunshows according to Bureau of Justice Statistics survey of Firearms Using Offenders (inmates who carried or used a firearm in the offense for which they were imprisoned)
2004 Source of firearms
11.3% Retail Purchase or trade
7.3 - Retail store
2.6 - Pawnshop
0.6 - Flea market
0.8 - Gun show
37.4% Family or friend*
12.2 - Purchased or traded
14.1 - Rented or borrowed
11.1 - Other
40.0% Street/illegal source
7.5 - Theft or burglary
25.2 - Drug dealer/off street
7.4 - Fence/black market
11.2% Other
* CNB note: Friend or family of a state prison inmate who is a Firearms Using Offender are often criminals themselves or at least aid, abet or associate with a criminal.