Uni-ball Signo 307 Gel 1919870 Rollerball Pen, 0.7mm Medium, Black Gel Ink, Pack of 3. Uni Super Ink Plus Nano Fiber Ink. The Signo 307 features a modern, checkered design at the top of the barrel. Delivers vivid, bold lines without skipping or blobbing even on glossy paper. Ergonomic, textured rubberized grip provides a comfortable and controlled writing experience.