LMAO.... all kids do it- unfortunately!!!! Especially this time of year when thier little noses are dryer! With my son I would ask him if he was digging for gold in there or treasures and give him this goofy look. Eventually he stopped out of embarassment I think.
With my daughter who just started this, she is 26 months, I started to make faces and ucky noises when she would do it. I then taught her how to use a tissue and now she will actually blow her nose or, I hate to admit this, pick it and put it in there (she used to wipe them on the dog though). It is a start and atleast most people are forgiving about seeing a baby digging away! lol
Also, with the weather changing and our houses being more dry thier noses get crusty and irritated and makes them want to stick thier lil fingers up and go digging. I have found just using the Little Noses saline spray definately helps. And having the tissue at hand helps since they think they are big girls and boys like Mommy and Daddy. My daughter actually likes the Puffs Plus Vicks!
Good luck with your little picker :) Know it will not last forever and that all kids do it, just some more discreetly! lol
Blessings to you and your family!