Neko Atsume: Kitty Collector is a mobile app where you place toys in a garden, which then causes different cats to appear and adorably interact with them. Once done, the cats leave Silver or Gold Fish (the game's currencies), and sometimes Mementos.
Unused early variants of the "cat has a flyer (ad) for you" graphics.
A chubby cat holding a flyer. The graphics in this gallery show different cats holding an identical flyer.Now on a platform, whatever this is supposed to mean.Two cats!?
Below are a couple of the used graphics, which all have the cats in the same pose.
Ginger, an in-game cat, holding a similar flyer in its mouth.Fred, another cat, assuming the same pose.
This needs some investigation. Discuss ideas and findings on the talk page. Specifically: According to the Neko Atsume Wiki's "Mementos" page, this object's name is "Soffted Hawk" (or possibly "Yellow Stuffed Toy"; the cat's page and the Mementos page are inconsistent here) with a description of "A stuffed yellow bird that you've seen somewhere." It's possible these are the English text present in the game's data, but they could also be translations (the wiki doesn't clarify this at all), so this should be looked into.
This Memento belongs to a cat named Hokusu-san (ほーくすさん, literally "Mr. Hawks"), which was provided exclusively during a 2015 promotional collaboration with the Japanese mobile carrier SoftBank. Unless you have an old SoftBank account and manage to get a pass (as the cat can only be obtained via their App Pass service), there is currently no way to obtain the cat or his Memento.
It's very possible that the cat was considered for a localized release at one point, as its English name in the game's data is "Kitty Hawks".