also: ハテナマーク
noun
Refers to the punctuation mark '?'. Used in everyday contexts, including computing and writing.
文の終わりにはてなマークを付けてください。
Please put a question mark at the end of the sentence.
クエスチョンマーク is a direct loanword from English, often used in similar contexts, but はてなマーク is more natively Japanese in feel.
From はてな (an interjection expressing doubt or questioning) + マーク (mark). The exact origin of はてな is uncertain, but it likely derives from the classical Japanese interrogative particle は and the particle てな.