Once penned, this special ink can only be seen and read in total darkness. When in darkness, any written or tattooed words, illustrations, or other marks made with this ink glow with a soft colored light. The normally invisible ink, while magic in nature, is undetectable by arcane means unless targeted by a detect magic spell cast with a 5th-level spell slot or higher. One bottle of shadow ink has enough ink to fill 10 pages with writing, illustrations, or other such markings.

"The man walked in broad daylight where it was safe. He smiled easily at neighbors and the crown's guard, and wore a jacket of red velvet with brown leather gloves. He seemed to love the sunlight, given his disposition. It was only in the darkness where he could be seen for who he truly was.

The man made a sharp turn into an overcast doorway. He knocked twice on the red door and waited. He pulled off the gloves absentmindedly.

The door opened a few moments later, revealing a darkened room and well dressed gnome inside. The two shook hands, and only from over the man's shoulder could it be seen: tattoos, scribed in a glowing ink, glowing on the back of the two men's hands. It was a strange mark, known only to a few: Thieves' Cant.

The gnome smiled and welcomed the man into the dark, where he truly belonged."

(Credits: the_griffons_saddlebag)