Berger may be wealthy, but he definitely is not the long-lost Koch brother.
In fact, if the 63-year-old lifelong city resident carried his own political sign, it too would read "Tax the Rich."
Berger is gaining national attention as a spokesman for a group called Patriotic Millionaires for Fiscal Strength, which advocates for what would amount to at least a 13 percent income-tax hike on people like themselves - Americans making more than $1 million a year.
A Democratic stalwart who has donated more than $300,000 to party and liberal causes since the beginning of President Obama's term, including $30,000 to the Obama Victory Fund in June, Berger says that a higher tax on the wealthiest Americans is a matter of fairness.
"To me, this was a way of shared sacrifice and doing something for the common good," said Berger, a critic of growing economic inequity in America, which has left the top 1 percent of the rich now controlling 42 percent of the nation's wealth.
Berger is not alone. More than 200 millionaires - including actress Edie Falco and Ben Cohen, of Ben and Jerry's ice-cream fame - have signed up for the group since it was formed in November 2010 to lobby, unsuccessfully, for ex-President George W. Bush's tax cuts for the rich to expire.
The group gained notice this summer when one member, a now-retired Google employee named Doug Edwards, asked Obama at a town-hall meeting: "Would you please raise my taxes?"
The president apparently listened, since he now says that higher taxes on millionaires is how he plans to pay for a $447 million jobs bill that he's been trying, unsuccessfully, to get through Congress. Berger has appeared on national TV with MSNBC's Ed Schultz and on local talk radio to push for taxing the rich at a higher rate.
Berger doesn't disclose how much more in raw dollars he'd personally pay if Congress enacted the higher taxes, but he said that most of his earnings come as direct income that's now taxed at 35 percent after the first $250,000. He said that he'd like to see income exceeding $1 million be taxed at 39.6 percent, the top tax bracket when Bill Clinton was president in the economically booming 1990s.
He said that conservatives like WPHT's Dom Giordano, who interviewed Berger, and some angry listeners who wrote to him afterward, always ask the same question: If he wants to pay more taxes, why doesn't he just write a check to the U.S. Treasury?
"It's not about me or any particular millionaire," Berger said. "It's about collective action" - raising enough money for the government to continue essential services and foster job creation.
Where does an affluent man like Berger get such progressive ideas? The simple answer is that it's in his DNA.
His mother, Harriet, was once a union organizer, and his father, the celebrated trial lawyer David Berger, who died in 2007 at age 94, came of age during the Great Depression and became a lifelong activist in the Democratic Party.
Serving in the Navy in the South Pacific during World War II, David Berger was startled to meet a fellow Philadelphian on New Guinea - Richardson Dilworth - who told him that if they survived the war, they should reform their hometown politics.
After Dilworth was elected mayor in 1955 in that decade's city-reform movement, he named David Berger city solicitor, and Berger later advised President John F. Kennedy on creating high-speed rail in the Northeast, which you may know as Amtrak.
Daniel Berger - who has one brother, Jonathan - came of age in the 1960s and '70s, when the progressive New Deal policies of President Franklin Roosevelt were still in force and the middle class prospered. He says it's no accident that when those liberal policies were reversed, so was the prosperity.
"That was a golden age for the middle class," Berger says of the post-World War II years when America built the interstate highway system and funded basic science, motivated by a space race with the Soviets. It was also a time when the richest Americans paid a top marginal tax rate as high as 90 percent, well above what the Patriotic Millionaires would advocate.
Berger has other interests - he's an avid tennis player, like his father, and he's developed a passion more recently for ballroom dancing. But none of that seems to consume as much as his political causes; he even sat down recently and wrote an 18-page paper detailing his ideas on taxation.
"Economic life by, of and for the top 1 percent is an old story in the history of world civilization," Berger wrote, "one which inevitably ends badly."