Uni-ball Signo RT UM-138 Gel Ink Pen - 0.38 mm - Lavender Black (Set of 2) Super practical and affordable, the Signo RT pens have been a long time tried and true favorite of JetPals. Uni Signo RT gel ink pens contain water-based pigment gel ink and feature a retractable 0.38 mm gel ink roller ball pen, rubber grip, and a steel point for strength.