Hmm..are you asking about on paper? For paper submissions, usually most writers use an official letterhead (I know some schools require it, like UNC) and if they do physically sign it, it's usually above their printed name. That's to the best of my knowledge at least!
When I found out about my missing signature, the admissions lady on the phone wasn't sure what was wrong with my letters at first. Apparently, they only see the letters. The evaluator's information isn't attached with his/her own letter. If it's a paper letter, I don't know if they would see a business card that was sent along with the letter..unless AADSAS scans that with the letter itself. I would call and ask someone who would know for sure though.