WALNUT CREEK (KGO) -- Fake posters that suddenly appeared on BART trains Friday morning are being called guerrilla art. They urge riders to watch their behavior.The rogue signs were taken down almost as soon as they went up. They displayed a message to BART riders.We showed the poster to some BART riders via smart phone."Something like that feels like a strong, positive answer, this is not not acceptable behavior," said BART patron Augusta Hopkins."I saw them on Facebook," said another rider Ryan Goldman. "This is a pretty interesting one. As an act of civil disobedience, on message."A BART spokesperson told us the signs were not authorized and were being removed from all trains, but continued on saying that the department is working on a campaign to help deter threats and show that BART is a community of riders that celebrate diversity."How you treat people is the way people are going to treat you. I'll just put it like that," added Rhonda Evans. "You disrespect a person and the person will disrespect you. Treat everybody equally, and they'll treat you back the same way. And I always have a smile."The person or group responsible for putting up the signs, has yet to come forward.