There is no responsibility in the act, but my advice to all public office holders--to you, of course, because you've asked--is that there is a risk in dealing with an unregistered lobbyist. If someone is coming to you and they are clearly representing someone else's interests, or even if they're working for a company and they're the director of communications, perhaps you could have your assistant check on the registry before they come over. See if you can find them on the registry. See if they're registered to talk to you about what they're coming to talk to you about. If they aren't, there may be consequences with that.
Again, as I was saying earlier, it's a risk management issue for public office holders.