Maybe what Google did[0], like:
X-Human: Work for us! {first 10-digit prime found in consecutive digits of e}@startup.com
[0] http://www.npr.org/templates/story/story.php?storyId=3916173
Re:Recruiting Humans with HTTP Headers
by graylights on Friday March 14, 2014 @02:48PM
(#7400939)
I don't even need a computer for that, just use leading zeroes:
0000000002
Very few people will see that link and it would be your onboarding process for new hires and it will save you time reading resumes and interviewing candidates.