Such pegs are often used to increase the visibility of a permanent survey point set in the ground. The permanent points usually come along as a steel pin, a round steel plate or a stone block at the roadside, but often are hidden below vegetation. When works along the road are in progress, the survey points are highlighted with such pegs. In such cases I map the permanent survey point as already said by @Tomas_J.
In other cases such pegs are set as temporary survey markers and either removed after work has finished or just left to disappear by the time. In such cases I do not map them at all, as proposed by @dieterdreist