The incident happened on Thursday, 8 April at approximately 130am on the route 32 bus at Kilburn Park. A man exposed himself to two women who were on the top deck of the bus.
He then got off the bus at Cricklewood Broadway.
Officers believe the man in this CCTV image has information which could help them with this investigation.
If you know who he is, contact the Met on 101 or tweet @MetCC quoting reference CAD5186/8April. Alternatively, call the independent charity Crimestoppers anonymously on 0800 555 111.