A newborn is observing, learning, differentiating and sorting without thinking about the passing of time, so I think the first key here is some simple consistency in giving him opportunity to become aware of your coming into his presence. With my first grandchild I saw weekly, I taught him his first word by raising my hand in greeting and saying "Abba!" with a smile every time I saw him and he first looked at me. You might just speak your nephew's own name or nickname rather than some other word, but it will likely not take long for him to know what to expect every time he sees you enter into his line of sight.
Rather than being concerned about being geeky or whatever, play on that a bit without taking it so far as to be scary or confusing. Reciting just a few lines of something like some Dr. Seuss poetry while adding some facial expression and vocal interpretation (funny voices) might eventually begin bringing out some smiles and even some giggles from him, and the same could be done with nursery rhymes or short songs. In whatever you do, however, do not place expectation upon him and be quick to try something different if he seems troubled or as he grows older. Overall, keep in mind he is observing, learning, differentiating and sorting in an ever-expanding world and you are hoping to ultimately be in tune with that and definitely more than a mere passing attraction.
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