If you are interested in becoming a Flagger. Goodwin William is providing professional Flagger Certification Classes. Construction companies need flaggers to control the flow of traffic around construction sites. Flaggers direct warning and detour signs, position traffic cones and barricades, and inform the construction crew of any safety hazards. If you are ready to become a flagger and need your certification, you need to apply for the position, schedule a time to come in and watch a training movie, and then take a 25 question test to get your certification.