Pistol Kanji

On certain weapons from Halo: Combat Evolved, Halo 3, and Halo 3: ODST you can find Japanese, Chinese or Korean characters on them.

Halo: Combat Evolved
Stamped onto Halo: Combat Evolved's M6D Pistol are two Japanese or Chinese characters: The Kanji and seven characters that can be seen only with the aid of a scoped weapon, such as the Sniper Rifle.

The first Kanji, stamped onto the top of the ejection port, is 七, shichi/nana (jp), or qi (ch) and, when translated, is the number seven (7).

The second Kanji is found on the bottom of the magazine floor plate, and is the character 力, chikara(jp) or li (ch). Meaning "strength" or "power", it appears to reference to how powerful of a weapon the M6D is.

Halo 3
In Halo 3, the M6G Magnum Sidearm features a Korean Hangul rather than a Japanese kanji. It is found on the bottom of the magazine and it reads 일곱 (il-gohb), when reflected. It translates to number 7.

Halo 3: ODST
In Halo 3: ODST, two Korean characters are stamped on the right side of the laser module on the M6C/SOCOM, which stands for the number seven.

Halo Living Monument
In the Halo Living Monument trailer the original 七 Kanji is clearly seen on the Commander's holstered M6 sidearm on the bottom of the magazine.