blue flag
noun
1
- a European award for beaches based on cleanliness and safety（欧洲）海滩“蓝旗奖”（根据清洁和安全程度评定）。
2
- Motor Racing a blue flag used to indicate to a driver that there is another driver trying to lap him【赛车】蓝旗（用于告知车手另一车手想超车的信号旗）。