Notice
Bulletin
noun, する verb
To display and indicate something is to put up a notice or bulletin.
けいじ
This is a jukugo word that uses the on'yomi readings of the kanji. You should be able to read this on your own.
アヤは、レストランが臨時休業の掲示をしている紙に余白があるのを見つけては、そこに落書きをします。
Whenever Aya sees that a restaurant put up a notice about shutting down for a holiday and there is some space left on the paper, she draws doodles there.