The incident is alleged to have occurred onboard a District line tube at around 8.20pm on November 26, 2025.
A woman boarded the eastbound service from Barons Court, taking a seat in a carriage when a man approached and stood over her.
The man is then reported to have sat down nearby, where he began to touch himself inappropriately over his clothing.
The British Transport Police reports that this was done whilst looking at the woman.
He left the train at Victoria.
Officers have shared a picture of a man they believe could have information that may assist their enquiries.
Anyone who recognises him is asked to text BTP on 61016, or call 0800 40 50 40, using the reference 700 of 26 November.
Information can be given anonymously to Crimestoppers on 0800 555 111.
