How would you address these people if the table they selected was in your section and you had to be their server?
I would love to say, "Hey moron, can't you read? We are supposed to seat you because obviously you can't do it without doing a shitty job." But I like making money more.
I generally go up to the table and cheerfully say, "Hello, would you like some menus?" And hope they make a connection but I think that may be too subtle.
DK/DC/I seat myself all the time: Have you ever had a Magnum ice cream bar? Did you love it?