Quote Originally Posted by Maple_and_PheonixFeather
Perhaps they use the personal question method that they used in HBP and DH...as they appear to be directed from the office and not from the public...
I doubt that would work. I only see two ways of implementing the system. One is that the questions and answers are known to the general public (i.e. anyone would know the correct answer). The second is that individual questions and answers are given to each member of the public. While magic would make this a lot easier I think that it is a lot of work to go through.

A couple of suggestions

Maybe it would be a badge, and then if the civilian taps it, it says the Auror's name and rank.
I think that this would work better if the person to touch the badge was its' owner. It might even attack if anyone else touched it. My other suggestion is that it might be reasonable to expect someone from the Auror office to be able to cast a Patronus. If the form of an Aurors patronus was known by the public it could be used as a test as Patronuses are unique. The problem with that is that a Patronus can change form.