USMC Regulations

Personal Protective Equipment (PPE)

The following PPE is mandatory for all persons operating or riding as a passenger on a motorcycle on DoD installations, and for all military personnel operating or riding on a motorcycle off installations, on and off road, in uniform or civilian clothes:
A properly fastened (under the chin) protective helmet which meets the standards of the Snell Memorial Foundation (SNELL), the American National Standards Institute (ANSI), or the Department of Transportation (DOT).
Impact or shatter resistant goggles or full-face shield attached to the helmet. A windshield, eyeglasses or fairing alone is not considered proper eye protection.
Hard-soled shoes with heels. The use of leather boots or over the ankle shoes is encouraged.
Properly worn long-sleeved shirt or jacket, long-legged trousers and full-fingered gloves or mittens.
The PPE for motorcycle operators during off-road operations should also include knee and shin guards or off-road Marine Corps boots and padded full-fingered gloves.

The above PPE is required.  If a Marine, a service member of any Service attached to a Marine Corps command, and a service member of any Service while aboard a U.S. Marine Corps installation, who violates the terms of this paragraph is subject to punitive action under the UCMJ for violation of this paragraph. Any such person who operates a motorcycle with a passenger who is not in compliance with the requirements of this paragraph is also subject to punishment for violation of this paragraph.