Hi There:
Well, being the Muesum President, I went through many anxious years as the Vice President of Modeling and Displays and Docent before that. Now there are thing we want the visitors to touch. Then there are many things that are definitely, Look but Don't Touch!
I think the best way I've seen to deal with this is our local LEGO groups. I belong to Texas Brick RailRoad in Austin. ( Don't make the meetings like I should though) and Tex-Lug San Antonio. ( Texas LEGO-USERS Group). We have signs that go on the displays. As You are all aware LEGO has MINIFIGS( Both the regular and the Newer(Dolls). There signs all the place. Please Don't Touch-It Scares the Mini-Figs!
Where the kids are concerned, at least the ones that try, it works ! We don't have too many finger incursions into displays. Now the trains at Shows and the Museum, LOOK OUT -It's the GrabbyFinger Monster! It happens everywhere I guess. I agree with some of the other posters though. We have an inate curiousity to fully examine parts we cannot see just looking. SO-we have to touch.
One year as a judge at an I.P.M.S. show I got very upset with a Judge picking up a model to examine it. He had on NO GLOVES, and he didn't ask the owners permission! Now I asked all those I could talk to before judging, that if necessary, as long as I wore gloves, could I handle their work. All but one or two said sure. The few that didn't explained why they didn't want the model handled. Good enough for me.
Other judges gave those models lesser points than I did. I personally feel that any model, is like the " MONA LISA"(La GIACONDA)-Ya don't just reach out and touch it. Why? Well, for one it's way older than your Grandma's House and second It would destroy the painting over time. Look-Don't Touch ! Is a good thing to follow. Just ask Sister Christina and her ruler !R.I.P. Sister-I still love you though!( Taught me well, she did)