Instrumental Weapon

The inverse of Instrument of Murder and Musical Assassin, Instrumental Weapon is where someone uses his or her weapon as if it were a musical instrument.

Compare Air Guitar. If you pack your weapon as if it were an instrument, that's Senseless Violins.

Examples of Instrumental Weapon include:

Film - Animation

Shaw from Open Season often plays Air Guitar with his gun Lucille.

Live Action TV

Super Sentai/Mighty Morphin Power Rangers: The Green Ranger calls his Dragonzord using his sword as a flute.
- One episode had a monster was defeated by Tommy playing his dagger and Kim playing on her bow.

Music

Vocaloid: Kamui Gakupo and his katana, which makes music when it is swung.

Video Games

World of Warcraft has the rare (and no longer available) Face Melter item which is an Ax that has frets and struts like an... Ax, which is to say a heavy metal rock guitar. It has an activatable ability that causes you to "rock out" with your Ax, complete with faux strumming and headbanging.
Team Fortress 2: the Pyro taunts with his melee weapon by strumming it as a guitar. The Medic taunts with his melee weapon, except for the Ubersaw and Solemn Vow, by playing it like a violin.
- In the Medic's case the sound varies depending on which bonesaw you're using. The Pyro makes the noises himself (unless he has the Third Degree, which produces a metal guitar riff).
In Lego Star Wars 2, when infiltrating Jabba's palace, you can build several stereos throughout the level that blast the Imperial March theme, to which the Gammorean guards will drop their fighting and rock out, playing their battle axes like guitars.
There's at least one Guitar Hero game where you can unlock Frostmourne and use it as a guitar.
The bard epic weapon in EverQuest was a sword that "sang". The graphic literally had notes coming out of it.
There's a glitch in The Legend of Zelda Ocarina of Time that allows Link to play his sword as an ocarina. This can be applied to any item used wile back-flipping after dropping and recapturing a fish.

Western Animation

Wile E. Coyote of Looney Tunes fame once played a bow and arrow like a harp while trying to figure out why it wouldn't fire. Of course, the plucking eventually did cause it fire at the worst possible moment.
In Adventure Time, Marceline plays an Axe-Bass, which is both a war axe (originally) and a bass guitar.

Real Life

Bows were used this way quite often; in fact, there is an entire class of instruments called 'Musical Bows', mostly found in Africa, which come from this.