CQ76 has a directory of different styles of 花押 and their owners
most importantly on 棗, a practise started by Jōō; either on the bottom of the lid, or on the bottom of the 棗
secondly, on the tubes of 茶杓; sometimes written on the line between lid and tube.
thirdly, on 花入; usually of the maker instead of someone favouring it. Usually in lacquer, or some layer of bamboo is shaved of and the 花押 written in ink
on lacquered or wooden 香合
on scrolls in ink
on 茶碗 in lacquer
on the underside of 水差し lid, also in lacquer
on the box of 釜, or sometimes cast into 釜 if made to order