Badass Creed/Web Original

SCP Foundation: "We Secure. We Contain. We Protect."
Protectors of the Plot Continuum: "Do not meddle in the affairs of assassins, for we are heavily armed and quick to anger. And not noticeably subtle."
The Dragon Ball Abridged version of the Ginyu Force has one.

Burter: "Speed of light and strength of all."
Recoome: "The Ginyu Force shall make them fall!"
Jeice: "We're King Cold’s army’s strongest force."
Guldo: "We’ll beat them all, secure the course!"
Ginyu: "If trouble meet us as we pass..."
Ginyu Force: "WE’LL SHOVE OUR FIST RIGHT UP THEIR ASS!"

"We are Anonymous. We are legion. We do not forgive. We do not forget. Expect us."
From RWBY, the passage Pyrrha recites when unlocking Jaune's aura in V1E7:

For it is in passing that we achieve immortality. Through this, we become a paragon of virtue and glory to rise above all, infinite in distance and unbound by death. I release your soul, and by my shoulder protect thee.