The correct answer is (D) Proof of genuineness; an official mark or stamp on an article of gold or silver to authenticate the metal's purity; any mark or sign of genuineness, good quality, etc. Also, any distinguishing characteristic or feature.

The tern, hallmark, derives from Goldsmiths' Hall, London (where the Goldsmiths company, which assayed precious metals, is located) + mark.

Examples of use:

• The loss of no men in that victory was a hallmark of his military genius.
• His uniform bore the hallmark of the royal house.