https://www.theverge.com/2018/2/17/17023738/facebook-election-ad-verification-postcards-russia

Facebook plans to mail out verification postcards through the US postal service to anyone purchasing ads related to US elections, according to Reuters. The postcards will contain a special code that advertisers must provide back to Facebook to prove they’re in the United States.

This new verification system will be required for all advertising that mentions a specific candidate running for a federal office — such as the presidency. It will be implemented in time for the mid-term elections this coming November.