What is the design on the pen at the top? Google Lens gave me this, which is tangential: https://en.wikipedia.org/wiki/Guilloch%C3%A9 https://en.wikipedia.org

What is the design on the pen at the top? Google Lens gave me this, which is tangential: https://en.wikipedia.org/wiki/Guilloch%C3%A9 https://en.wikipedia.org/wiki/Guilloch%C3%A9