* "Semper Fidelis" (Latin for "Always Faithful") is the official motto of the United States Marine Corps. It represents the unwavering loyalty and dedication Marines have to their country, their Corps, and their fellow Marines.
* "The Few. The Proud." is the unofficial motto of the Marines. This slogan emphasizes the elite nature of the Marine Corps and the dedication and courage required to be a Marine.
You might also be thinking of their slogan, "Marines - The Force in Readiness." This slogan is used in recruiting materials and emphasizes the Marines' constant preparedness for any mission.