Peter Austin, managing director for London Overground Rail Operations Limited (LOROL), said:
"We are disappointed by the result of the ballot, but would highlight that fewer than half of our 124 conductors voted, and only 43% of those voted in favour of industrial action.
"We believe industrial action is unnecessary. LOROL continues to give the RMT assurances on employing conductors in alternative customer service roles and offering a generous voluntary redundancy package to those who want it.
"We urge the RMT to work with us to maintain progress in safeguarding jobs and avoid disruption to passengers."
More top news
Two members of the public were injured along with two police officers who were in the unmarked vehicle.
Scotland Yard recorded 1,235 Islamophobic attacks in the last 12 months, compared with 811 in 2015.
Officers say the child, aged two, was targeted in the Lewisham Shopping Centre.