Flower seal - Kaoin

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[Samurai and commoners' signatures]
Next, as the Ashikaga style became more common among samurai and commoners after the Northern and Southern Courts, around the 16th century, the trend of the noble kao mentioned above began to reverse, with kao with fewer strokes and easier to understand stroke order, that is, kao that were easier to write. Also, the trend of stamping seals on documents, which began among some Zen monks around the Northern and Southern Courts, spread to eastern feudal lords such as the Imagawa and Hojo from around the 16th century, and the trend of using seals instead of kao strengthened. This trend in turn influenced kao, leading to the use of (1) kao types such as engraving a kao on a block, applying ink and pressing it, or engraving a kao in a double hook style (kagoji style) and then filling it with ink after pressing it, and (2) kao seals, which were incorporated into seals as if they were seal inscriptions, and so on. It is said that the kao-gata technique for printing was first used in China during the Yuan dynasty, and examples of its use have been reported in Japan as early as the late Kamakura period. During the Warring States period, its use was known to have been seen among people such as Iwaki Chikatake of Oshu and Ashikaga Takamoto, the Koga kubo.

*Some of the terminology explanations that refer to "kao-in" are listed below.

Source | Heibonsha World Encyclopedia 2nd Edition | Information

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［武家･庶民の花押］
　次に武家および庶民層では南北朝以降足利様が普及する中で，ほぼ16世紀ころから上記の公家花押の趨勢とは逆に，筆画の少ない筆順のわかりやすい花押，つまりは書きやすい花押が多くなる。また南北朝ころから一部禅僧の間に始まった印章を文書に押捺する風がやはり16世紀ころから今川，北条ら東国の大名に及び，花押に代えて印章を用いる傾向が強まると，この傾向が逆に花押に影響を与えて(1)花押を版刻にして墨を塗って押したり，花押を双鉤式(籠字（かごじ）式)に刻して，これを押した上で墨を塡めるなどの花押型や，(2)花押を印文のごとくみなして印章に取り入れた花押印などが用いられるようになる。版刻の花押型は中国の元代に使用されたといい，日本でも早く鎌倉時代後期に使用例が報告されているが，戦国時代になると奥州の岩城親隆，古河公方足利高基以下の使用が知られている。…

※「花押印」について言及している用語解説の一部を掲載しています。

出典｜株式会社平凡社世界大百科事典 第２版について | 情報