Signo DX Gel Ink Pen | Uni-ball

To be very specific, it's the .38 Uni-ball Signo DX UM-151 Gel Ink in Blue-Black (navy) ink.

I know .38 is not for everyone, but architects, for one, will like.

Pair with navy Leuchtturm 1917 B5 softcover notebook with dotted pages (see rec) for analog list-making and note-taking to your heart's content.