uni-ball Signo 207 Retractable Gel Pens, Medium Point, Assorted Ink, 8-Pack – Link

This is currently priced at just $6.29 on Amazon, which is the lowest it has ever been.

• Uni Super ink is specially formulated to become trapped in paper, helping prevent criminal check washing and other document alteration.
• Textured grip provides superior writing comfort and control making this pen truly a pleasure to write with.
• Stylish metallic accents with a high-quality finish.
• Archival-quality, acid-free ink is quick-drying and fade- and water-resistant.
• Stainless steel, retractable tip for added convenience.