Frog 蛙

This fellow is a fairly common little graffiti work, but you have to hunt for it and it might pop-up in some unexpected places. Frog in Japanese is "kaeru," which is the same sound for the verb "return/to return" (also "kaeru") but both are spelled differently using different kanji/kana. Which gives rise to the pun:

お金が返る。(Money returns)

Which sounds like,

お金が蛙。(Money is frog)

Honestly I don't 'get-it' but I have a real difficult time with japanese humor, which is often wordplay especially in Rakugo, but is also present in Manga, Anime, and of course a night out drinking with Japanese friends.

The frog goes: ケロケロ (kero kero).