This appears as a fine quill pen, in excellent condition. It will radiate faint magic. Poison Pens were originally assassination tools, created during an age when poisoning one's enemies was considered more civilized than bloodshed. Many of them were produced at that time, but most are now lost. While the process of making them was well understood by mages and others, inevitably, some were made with poor quality control.
The idea of the original pen was that any letter or note written with it would, after a period of an hour or so, become poisonous to the touch. The ink used could be quite ordinary, but after the onset time, touching any of the words, or even the paper they were written on, would allow a semi-magical poison to be absorbed through the reader's skin. A particularly dreadful substance, the victim had to roll a Saving Throw versus Poison, or take 1d6 HP damage immediately, and 1 HP per minute thereafter until cured or dead. A successful Save induced 1d6 HP of damage immediately, but caused no further harm.
This version of the Poison Pen is one of the flawed ones; it activates not in an hour or so, but within seconds. The writer of the letter or note must roll a Saving Throw as if they were the target of the missive, not the sender. Wearing gloves while writing or reading will protect against the poison.
Optional: Wearing gloves while writing or reading will not protect against the poison!
Image: Dustyfeet studios, bottle, pen and ink bottle by Pierre Bamin, released under the Unsplash License, and modified in Inkscape by David