遺憾 / 判子。

「印鑑」という物と「判子」というのはどう違いますかと考えます。Both seem to mean "seal", and both turn up a lot of likely images on Google (inkan, hanko). Wikipedia says, "Inkan is the most comprehensive term; hanko tends to refer to seals used in less important documents." That makes sense given 子 (child) as the second kanji of 判子.　All the subclasses of seals for personal use seem to include 印, which (as 判 seems to do) means an actual seal. Wiki also says that there are inexpensive, prefab seals, called 三文判 (sanmonban), available at stationery stores; there's that はん　from 判子, so that's more support for hanko as less "weighty" versions of inkan. Wiki says that 三文 derives from the mon, a unit of currency—a three-mon seal, a cheapie. Wonder whether there's any relationship with the family crests, mon, worn on kimono—one, three, or five, with increasing degrees of formality. The "mon" kanji root is the same—in the kimono version, it's mon 文 with ito (thread) in the hen position (紋).

Kinda also makes me wonder whether there's any relationship between 門 "mon", phonetically a circle/circular object (unit of currency, or a crest) but in this kanji gate, and 円 (maru/en), meaning a circle/circular or a unit of currency (yen) but very similar structurally to 門.　Neither of them remotely circular in shape. 面白い。