It bothers me when a coworker who is talking with me at my desk reaches out and stabs a finger into the screen, leaving fingerprints/skin oil (sometimes repeatedly and lingeringly rolling that finger around for emphasis). You can't see the marks, maybe, but later, as the sun moves into the right position, what seemed invisible becomes a slew of very visible scattered smudges making my monitor look all dirty and hard to read.
I've said up to at least two times each to different people who were touching my screen something like (trying to be mild in tone and phrasing), "I'd rather you not touch the screen" or "please don't touch the screen", and the person always says "oh, sorry". But the next week, there comes someone doing it again.
I thought about having screen cleaning materials out and very obviously cleaning the screen where they've been touching immediately after they do it, but I'm worried that is too passive-aggressive an approach.
I thought about trying to sit in my chair in a way that blocks the person from reaching the screen, but that's not workable the way I have a straight desk open on the sides.
I considered just consistently asking the person each and every time to not touch the screen, but I don't want to be offensive. I also tend to come across about 2 or 3 notches more upset or angry than I really am, and people tend to notice this and react unless I really make an effort to be mild—but this leaves me usually saying nothing. I'm concerned people will go tell stories to others about me freaking out about my screen. (Whether or not I do freak out or my reaction is more than they think it should be, it seems a simple problem that is solvable, I just don't know how. I think it's reasonable to want people to avoid dirtying/marring, even if temporarily, the work tools assigned for my use.)
Besides not having these conversations at my desk (we could go to a conference room or to the other person's desk where I for sure will not be touching their screen), or putting up some kind of physical blockade, what are some strategies I can use to be tactful, mild, yet effective?
Note: I shouldn't have asked this question at work because someone came by, saw what I was posting before I could switch to another tab, and deliberately dragged his finger across my screen to bait me. Sigh. Anyway, here's the question.
I just thought of getting a small pointing device, something like the stylus for a tablet. I could attach it to the monitor with a small piece of adhesive Velcro. What do you think about, when someone starts touching the screen, to hand this to them and ask them to point with it?
Photos added for reference.