Twitter's latest marketing campaign is raising questions about whether the San Francisco-based company broke the law.
The guerrilla marketing advertisements can be seen on San Francisco sidewalks. Residents and visitors can also see the ads everywhere at the Powell Street BART station. It uses people's tweets about Twitter.
The ads are found on walls and even on columns. But it's another place they were found that is triggering some controversy and an apology from Twitter.
In the Tenderloin, steps from where people are sleeping on the streets and in tents, Twitter has stenciled tweets on sidewalks.
"I think it's in poor taste," said Sidney Cox, who lives and works in downtown San Francisco.
It appears to be part of the social media company's big new marketing campaign inside the Powell Street BART station.
"It's vandalism," San Francisco-resident Kirk Linn-Degrassi said.
The stenciled tweets have sparked strong responses both on Twitter and on the streets of San Francisco.
The city also said it's against the law.
"That's graffiti vandalism and it's very illegal," said Rachel Gordon, San Francisco Public Works spokesperson.
Gordon said companies can't use sidewalks as billboards.
"They have no permission to do this, they're not going to get permission to do this, nor is any other company going to be able to come and use our sidewalks for commercial purposes," Gordon said.
Twitter responded with the following apology: "We looked into what happened and identified breakdowns in the process for meeting the cities' requirements for our chalk stencils. We're sorry this happened."
The city said this is not the first time a company has done something like this and it makes no difference whether the stenciled tweets are chalk or spray painted. If city crews have to remove the stencils, Twitter will have to foot the bill.