Far-right symbols “possibly linked to the attacks in New Zealand” were spray-painted on a wall near a school, police said.
Thames Valley Police is investigating after the graffiti appeared in Cheney Lane, Oxford, on Saturday.
Images taken by the Oxford Mail newspaper show two swastikas as well as the words “sub 2 pewdiepie” on the wall near Cheney School and Oxford Brookes University.
The symbols appeared just a day after the massacre at two mosques in Christchurch which left 50 people dead.
The expression appears to refer to words uttered by the gunman during his live-stream of the killings, who can be heard saying “Remember lads, subscribe to PewDiePie” in reference to an internet meme.
YouTuber PewDiePie, real name Felix Kjellberg, said later he felt “absolutely sickened having my name uttered by this person”.
Superintendent Joe Kidman said: “I deplore the actions of the person or persons responsible for this graffiti and there are no excuses for those who carry out hate crimes.
“Oxford is a tolerant community with strong links between our faith communities.
“This act is not representative of the people of Oxford and it will not be tolerated by Thames Valley Police.
“We are aware that the awful events in New Zealand will have heightened concerns for many communities.
“As a result officers in Oxford as well as the wider Thames Valley, will be visiting places of worship to reassure all faith communities.
“I have personally also made contact with a number of our faith leaders to offer support and advice on reviewing their safety and security measures.”