Ater filling out a check, the writer rolls the protector over the dollar amount or signature, and the steel teeth on the wheel perforate the check, making it impossible for someone to tamper with the writing. Additionally, under the wheel rests a small sponge and ink reservoir which was designed to dispense red ink while the wheel rolled. The ink soaked through the edges of the cut paper to further render the check cheat-proof. The company created the pens in black hard rubber, chased black hard rubber, red hard rubber and red and black mottled hard rubber in sizes two through six, plus a giant size. A few rare pieces in plastic have also been seen, some without the check protector in the cap.
Collectors can further identify Security pens by their unique clip.
If you start scavenging for Security pens, this may be the first time you save money by browsing the vintage stores. Roller ball pens are sort of a cross between a ballpoint and a fountain pen and use water-based ink. The advantage of the roller ball is that it combines the nice smooth writing of a ballpoint with the vivid wet ink line of a fountain pen. One disadvantage the roller ball inherited from its fountain pen ancestry is the ink s lack of water resistance. What holds true for fountain pen ink is generally true for roller balls.