This is a very interesting question, and one I had never anticipated.  I guess somehow I thought everyone who went on a wilderness trip wanted to get away from people!  Especially people they don't know.

If someone approached our campsite (we are a traveling couple, just two of us always) asking for directions or about a portage, we would be polite and answer questions, but it wouldn't really occur to us to invite that person into our camp.  Perhaps it is the mentality of traveling as a twosome; it is hard for me to imagine traveling with a group of three canoes and several tents, too!

I like to speak with people on the portages and occasionally ask what they thought of a portage if they have just come from the other direction.  I do that more now that I have old-lady knees!  And I do find that some people seem glad to talk and others are reticent.

We are of course cordial to the US Forest Service personnel who occasionally stop by.   :)

Good luck with your welcome flag.  I will be interested to see if you get any response.