Here's the section of AE Reg 190-1 (Driver and Vehicle Requirements and the Installation Traffic Code for the U.S. Forces in Germany) dated 4 December 2008:
5-6b. MOTORCYCLE SAFETY
(6) Motorcycle operators and passengers will wear—
(a) A helmet properly fastened under the chin. Helmets must meet the standards set by the American National Standards Institute, the Snell Memorial Foundation Standards, the Institut für
Zweiradsicherheit e.V. (Institute for Two-Wheel Safety), or the Economic Commission of Europe for bicycle helmets.(b) Eye protection. Eye protection must meet the Vehicle Equipment Safety Commission Regulation standards or the European equivalent. Eye protection must be impact- or shatter-resistant
goggles or a full-face shield properly attached to the helmet. A windshield or eye glasses alone are not proper eye protection.
(c) Protective clothing. Clothing will include clothing required by DODI 6055.4, the Institut für Zweiradsicherheit e.V., or the European equivalent—
1. Full-fingered gloves.
2. High-visibility garments (bright-colored clothing (for example, yellow, bright green, red, orange) for day travel and reflective clothing for night travel). When wearing military uniforms,
military operators will wear a brightly colored reflective PT-style vest that is clearly visible from the front and rear of the motorcycle. Operators in military uniform may also wear brightly colored approved motorcycle riding jackets. The Army PT jacket worn with an orange or yellow reflective belt (worn diagonally across the shoulder) meets both day and night requirements.
3. Over-the-ankle footwear according to DODI 6055.4, paragraph E3.2.7.1.3. Footwear should be made of sturdy leather and have a good oil-resistant sole to reduce slipping hazards. Service
boots meet this requirement.
4. Long-sleeved shirt or jacket.
5. Full-length trousers.
By the reg, you have the option of wearing either DOT, Snell, or, ECE. Keep in mind that this may only apply to Germany and other NATO countries. Not all of our non-NATO neighbors recognize the Status of Forces Agreement(SOFA) which is why you need an international license to drive in Poland, for example. Your USAREUR license in only good on Germany and other NATO nations.
Hope this helps. The reg is located at
http://www.divisions.imcom-europe.army.mil/sites/safety/docs/aer190-1.pdf.
Also check out IMCOMs Army Traffic Safety Training Program (ATSTP) at
http://www.imcom-europe.army.mil/sites/management/so_atstp.asp for more information.