The Casino Seal is a seal that glows when it detects the use of chakra nearby.

Hazou got the idea for this seal in Chapter 18, when he scouted casinos for making money at and noticed seals of unknown function in one of them:

"What does security look like at the casinos?" Wakahisa asked.

"Varies a lot," Hazou said. "I checked three different casinos. […] The third place was the most upscale, but I didn't see anything but civilians guarding it. It did have a bunch of seals scattered around the ceiling and the tables, disguised as patterns in the wood or whatever."

Hazou did not finish developing the seal until Chapter 217B.