Abstract: A safety signal warning flag device for mounting on bicycles and other pedalled wheeled vehicles, in order to make them more visible to motorists, other cyclists and to pedestrians for mutual safety. The device includes a flag pole with a highly visible colored flag carried on one end of the pole, and the other end of the pole engaging a supporting base carried on a rear mudguard or fender of the bicycle. The device includes a universal swivel joint in which there is a spherical member secured to the lower end of the flag pole, and a hollow socket member forming a base on the fender, so that the flag pole can be swiveled into any desired angular position, to indicate the location and presence of the bicycle to warn motorists to keep their distance therefrom.