疑問符

1. Origins, structure, and basic meaning

• Structure: 疑問符（ぎもんふ） combines 疑問, a question or doubt, with 符, a sign.
• Basic usage: It names the question mark ?, used at the end of a sentence or to flag something not understood.

2. Common pitfalls and similar expressions

• A question versus its symbol
  • 疑問 can refer to a question or the content of a doubt; 疑問符 is the symbol used to mark it.
• Adding and writing in a mark
  • 疑問符を付けた says a mark was added. 疑問符を書き込んだ more specifically describes writing it into a text beside an unclear part.