I have a few kids in my class who have their fingers in their mouths all. the. time. My standard approach is to ask them to please go wash their hands, then bang my head on a wall. Sometimes we even break out a pair of winter gloves after the twentieth time. It serves as a good reminder.
Side memory: I used to have a boy, Michael, who always had his finger jammed up his nose. He wasn’t even picking it, just plugging it. I would out band-aids with hearts to remind him that ‘loving finger stay out of noses’ or some such nonsense, and not two minutes later he had his bandaged finger in his nostril. “Michael, why are you doing that?” I asked in exasperation. He shrugged and said, “I just like it.”
Well, it’s hard to argue with that.
Anyway, the mom of one of my current thumb-suckers started using Thum, a nail-polish-type stuff that tastes bad, and darned if her son had non-saliva-coated hands the next day! She hasn’t been keeping up with it, though, so I bought my own bottle and am going to ask if I can give him a manicure when the need arises.