On IRC it's easy, point them to your "contact me" page, and invite them to contact you, and you can reply to the email, or answer their IM or skype call or whatever. It's a fairly safe assumption to make that you are the only person capable of modifying these web pages. In person, if you have "blog cards" or somesuch, then print a secret URL on them, only available on the card. Print on the card somehting like "the secret word is 'cyrrhosis'" or something more pleasant, and leave a page on the URL explaining that this page is to help people verify your identity, and the the secret word is 'cyrrhosis'. Alternatively, just write a blurb on that page and say "The 8th word of the second paragraph is..". You may need to print this on the back of the card, though. As a rule, people tend ot take me at face value when I say I'm Moof, though this is because they tend to know me from IRC.