Meek Mill may be in prison for violating his probation, but he's also everywhere you look.

The Philadelphia street rapper's image is all over the streets of Philadelphia, on billboards and newsstands, and on wrappings around SEPTA buses, along with messages asking people to "Stand With Meek Mill" and hashtags seeking that the 30-year-old rapper, who's currently at Camp Hill State Correctional Institution doing two to four years, be released.

Who's paying for all billboards and wrapped buses? Credit is given in the fine print in a driver's sight on I-95 and the Vine Street Expressway: "Paid for by Michael Rubin, Roc Nation & Friends."

Roc Nation is the management company owned by Jay-Z, which counts Mill, who appeared with the headlining superstar at this summer's Made in America festival on the Ben Franklin Parkway, as one of its premier clients.

Speaking from New York on Wednesday night, the Lafayette Hill native said the billboards have gone up "to create awareness so we can get this solved. I believe this will quickly rectify itself."

With the public campaign in support of Mill, "there are now millions of people watching this," Rubin said.

He wasn't sure how many billboards were on view — the final tally is six billboards, three bus ads and 18 bus shelters and/or newsstands, according to a Stand With Meek Mill spokesperson — and wouldn't reveal how much money he's spent on Mill's cause. But he spoke as if it was no object.

"If we need one on every corner in every street in the state of Pennsylvania," he said. "we will do it. We won't quit."

The billionaire says both his and Jay-Z's support of Mill is "unwavering." Roc Nation did not respond to requests for comment.

The effort was born last week, after Common Pleas Court Judge Genece E. Brinkley sentenced the rapper to two to four years in state prison for probation violations related to a 2008 weapons and drug charge. The perceived harshness of that sentence has provoked outrage among Mill's supporters: On Monday evening, a Free Meek Mill rally was held outside the Criminal Justice Center, with advocates including 76ers great Julius Erving, Eagles players Malcolm Jenkins and Jalen Mills, and hip-hop mahoff and Maybach Music boss Rick Ross showing their support.

The next day, Meek signage showed up around town: A photo of the 30-year-old rapper with hands held together as if in prayer looking skyward and the all caps message "STAND WITH MEEK MILL," along with the hashtags #Justice4Meek and #FreeMeekMill.  The ads also direct fans to a Change.org petition imploring the Pennsylvania Board of Pardons "to close review Meek's application for Pardon and have his unjust prison sentence remedied." As of Thursday morning, over 373,000 had signed.

The main objective of the campaign is "to get Meek out of jail as quickly as possible, to make sure he doesn't spend a minute more in prison than he has to," said a spokesperson for the Stand With Meek Mill campaign. "The second goal is to use his platform to make people aware of the sentencing guidelines and the parole issues that effect lots of people."

Rubin called Mill is a close friend who has "been over my house dozens of times. I think he's a great guy who's making very positive contributions to our world. I'm a big believer in him and I'm sure of it."

He called the rapper "a uniter, not a divider."

"If he did anything that I thought was remotely wrong, I would never stand behind him," Rubin said.

He spoke on Mill's behalf during last week's hearing, and believes a miscarriage of justice occurred when the judge sentenced Mill despite recommendations against prison time by the rapper's probation officer and the District Attorney's Office.

Mill's predicament is uniquely unjust, Rubin said, because of the recommendations against jail time. "If you talked to a thousand people in the legal community," he claimed, "a thousand out of a thousand would say he shouldn't be in jail."

Rubin said he had talked to Mill once since he's been in prison.

"His head is up," Rubin said. "He believes that this is a good world, and he's a good person who got caught up with one bad judge. He's got a good head on his shoulders."