This is the gold medal for 15 years of service in the national’s people’s army of the DDR. They started with this type of medal in 1956 and stopped in 1990.
Faithful Service Medals with a similar design were issued by Border Guards (Grenztruppen) and Civil Defense (Zivilverteidigung).
There were 4 different medals for this purpose;
Bronze: 5 years of service (no stripe)
Silver: 10 years of service (white stripe)
Gold: 15 years of service (yellow stripe)
Gold: 20 years of service (gold stripe and Roman numerals XX)