Maybe everybody but me knows this style, but just in case I'm not the only one:
I went to a local nail salon today to interview the owner for an editorial mention in a local free magazine. She showed me some detailed designs as samples which she said were trendy and painted onto just the ring finger of each hand.
She explained that she uses ordinary artists acrylic paint and a tiny paintbrush and paints onto the nail varnished surface, and then puts a clear topcoat over the nail to seal the design on.
I had a go when I got home and it was easy and looked great. OK, she had tiny hearts and a Christmas tree and I just did three little dots down the middle of my ring fingers but still, it's free if you have any acrylic paint at home.