Hi Brian,
I'm assuming you've set the login page as your "default page"? Or not?
Personally I don't get too worried about this sort of thing. If you watch your server for any length of time you'll see dozens of attacks pretty much daily. You'll also see Googbots and the like spidering through your (public) site and so on. This is all pretty "normal" web traffic.
Sure it can be exciting the first time you see it happen, but it's pretty much ops normal, and to be expected. You've opened a port - people are sending requests on that port - it's kinda just working as it's designed to work.
Of course, assuming you've kept your NetTalk reasonably up to date, the attacks fail. Short of brute-forcing the login screen, I'm not aware of any attack vector that will succeed.
cheers
Bruce