The Met police have launched an investigation after posters of the union jack being set on fire were put up at a bus stop in west London.
Paul Pavli, who works in the area, told BuzzFeed News he saw police officers with a forensic team at the scene.
"Someone had lifted up the actual frame, and put it underneath, so it looked like a proper [advert]," he told BuzzFeed News.
"I was angry about it. It felt like someone just wanted to stir up more trouble, especially in light of what's just happened in London," he added. "Why would someone do that?"
The Met police confirmed to BuzzFeed News that officers were called to the scene on Thursday shortly before 10.30am. "Transport for London attended and removed the poster," a Met police spokesperson said. "A forensics officer examined the scene and retrieved several exhibits for further examination."
Reports on social media suggest several bus stops around London were hacked shortly after the attacks in Westminster on Wednesday evening. However, police appear to only have knowledge of two in west London.
A Met police spokesperson told BuzzFeed News that a member of the public reported two offensive posters, which had been placed inside a bus shelter in Ladbroke Grove.
The spokesperson also said the matter is not terrorism related, but is being investigated for inciting racial hatred. No arrests have been made.
A Transport for London (TfL) spokesperson confirmed to BuzzFeed News that the posters were "not an authorised advert". TfL has also instructed contractor JC Decaux to remove any of the unauthorised found on its network.
"It is flyposting and an act of vandalism," the spokesperson said. "We take this extremely seriously and have reported the incident to the police. We have also instructed our contractor to immediately remove any found on our network."
BuzzFeed News has seen an email from a JC Decaux representative to a member of the public, which says there is currently a big operation on social media by "illegal creatives" to hack bus shelters across the country.
The email also says JC Decaux had worked with the police on Thursday morning to remove the poster in Ladbroke Grove and others around London.
BuzzFeed News contacted JC Decaux but they have refused to comment.