There are two things that clue me in - attention to detail and the ability to follow directions. I give a test that has explicit instructions and it works every time. The test has both math and non-math problems but is mostly logical. The questions are more broad so that I can see their thought process.

I also weed candidates out immediately in the job description by throwing in a sentence in the middle that instructs them to send their resume with the subject line "entropy" or some other key word. When I get emails with resumes I simply delete those that don't have the key word.