The probability that you have heard of this is effectively close to zero. I couldn’t believe it when I heard it myself.
There is such a thing as an ‘American smile’. I learned this on my most recent trip to Tokyo. I was sitting, in the early evening, with a long time friend of mine who was playing his guitar and singing ‘oldie’ songs. I took a picture of him and he asked if I wanted an ‘American smile’. Which he proceeded to show me.
I told him I had never heard of an 'American smile'. He said it was commonly known and discussed among Japanese who travel. To prove his point he stopped a young woman who was passing by and asked her if she knew what an American smile was. She said 'Yes'.
We both invited her to sit down. She was taking her dog for a walk and had time. She noticed his guitar, a miniature, and ask to strum it. Which she did for a few chords. I then asked her for a photo with an American smile.
For you who are surprised, as I was, I found ‘American smile’ in wikipedia when I was in Japan. I can’t find it now that I’m back in the U.S. For wikipedia, my computer, connected to the Japanese Internet, said I was in Japan.
One reason I never heard of it is that I’m a deeply happy person, so I see smiles on everyone around me, whether they have one or not.
And yes, beautiful Japanese women will sit down at an outdoor coffee shop with me, a Japanese man, and my American girl friend, if you speak Japanese and don't look threatening.