Uni-ball Signo Gel Ink Pen, Black, 0.38mm, Pack of 10 Uni-ball Signo DX (UM-151) 0.38mm tip size. Users can enjoy clean and even flowing lines, and the strong tips can withstand all the heavy handed writing you can offer. The Uni Signo DX is highly sought after by artists and writers alike, but difficult to find in the US.