Did you try looking in AR 600-8-22? If you did, you would have found:
1. Description: The Army Overseas Service ribbon is 1 3/8 inches in width. It is composed of the following vertical stripes: 3/16 inch National Flag Blue 67124, 5/16 inch Grotto Blue 67165, 1/16 inch Golden Yellow 67104, 1/4 inch Brick Red 67113, 1/16 inch Golden Yellow, 5/16 inch Grotto Blue, and 3/16 inch National Flag Blue.
2. Components: Ribbon. MIL-D-11589/282. (There is no medal for this ribbon).
3. Criteria: a. Effective August 1, 1981, the Army Overseas Service Ribbon is awarded to all members of the Active Army, Army National Guard, and Army Reserve in an active Reserve status for successful completion of overseas tours
if the tour is not recognized by the award of a service or campaign medal.
b. The ribbon may be awarded retroactively to personnel who were credited with a normal overseas tour completion before August 1, 1981, provided they had an Active Army status on or after August 1, 1981.
c. Requirements for award of the ribbon are contained in AR 600-8-22.
4. Background: a. The Army Overseas Service Ribbon was established by the Secretary of the Army on April 10, 1981.
b. Subsequent tours will be indicated by the use of numerals.
Therefore, depending on the length of tour in Germany, according to this regulation you are not authorized to wear it yet. I know Hawaii was a 3 year tour when I was there, but I'm not sure about Germany.