Gallow was accused of pulling out his gun and pointing it at a woman and her 2-year-old daughter on June 5.
Police say the victim, Chastity Cancel, was driving on Randall Avenue when the driver behind her started flashing his lights and honking.
Cancel, who was reportedly trying to merge into traffic, responded by making an obscene gesture at Gallow.
Eyewitness News is told the off-duty officer pulled up to her vehicle, pointed his weapon at her and cursed at her. A frightened Cancel yelled at him that she would write down his license plate.
The officer allegedly followed her for at least two blocks, waving his gun, before driving off. Cancel wrote down his plate number and called 911.
Gallow, who is assigned to the 28th Precinct in Harlem, was suspended without pay for 30 days. He has been a police officer for almost six years.
NEW YORK AND TRI-STATE AREA NEWS