This discussion peaked my interest, so I went back and scanned all the badges I have going back eight years.
What I found was that every badge, at least from 2008 and on, includes your name, full address, phone number, email address, and badge confirmation number.
Starting in 2012, the bar code also includes what looks like a public-key encryption string. I'm not sure what that was used for.
So yes, if you let a vendor scan your badge, they will have a lot of personal information about you.