Signo Gel RT
Used by 2 peopleamazon.com ↗
“I like Uni-ball Signo Gel RT pens, but I keep losing them.”
Martin O'Leary Interview, Artist, developer · via Uses This 
“Currently: an unlined soft cover Moleskine and a 0.38mm Uni-ball Signo RT (black).”
John Gruber Interview, Writer (Daring Fireball) · via Uses This