A few years ago, the National Aquarium of New Zealand went viral with their Naughty Penguin of the Month signs. The idea caught on elsewhere. Heaven on Earth Cat Rescue in Los Angeles has a title for the nice cat of the week and the naughty cat of the week, posted with pictures and the reasoning behind the designation.
You can imagine that these glimpses into each cat's personality will help them find "furever" homes. Kallo in particular looks like a delightfully mischievous soul.
Felix, on the other hand, will require a talk with shelter volunteers. This picture makes him look as if he's either ashamed, or (more likely) upset that he was caught. It's possible that what he did was minor, but not proper to put on a public sign. At any rate, you'll enjoy seeing a collection of 20 naughty cat of the week signs (one cat got a whole month) at Bored Panda. By the time you've read through them, you will feel like you know these cats well.