Referral field in Aeon registration form

We're considering adding a referral question to our Aeon registration form. Something along the lines of "How did you hear about LSU Special Collections?" with several drop down options (e.g. LSU website/catalog, digital collection, print/radio/tv, social media, in-person, return visitor, other...). 

Has anyone else tried collecting referral info in Aeon? If so, have you made it a required field on the form? I'm also interested in looking at other institutions' referral options to ensure we're covered a broad range of sources. 

Thanks,

Amanda (Louisiana State)