Unsanctioned memorials are popping up all over the mountains. Depending on where it is, don't be surprised to see it has been removed. Someone put a plaque dedicated to a loved one, complete w/ picture of the deceased, on a trail on Mount Clay last year. As far as anyone knows, there was no connection to the mountains other than she loved them. This is illegal, and I'm pretty sure the plaque was removed by the USFS. In wilderness areas the USFS has gone so far as to, get this, CUT DOWN TREES WITH BLAZES to keep the hand of man invisible. On Owl's Head the blazes, signs and cairns have been removed because it is in a federally designated wilderness area.
If the 911 memorial on Mt. Washington is in the State Park Area it might be left alone, not sure. If it's outside of the boundaries of the park, I'm guessing it will go. For a real mountain tribute to the 911 deceased, folks may want to get involved with this: