"If the world were a bank it would been saved long ago," read the yellow banner on the bank's gray glass tower, which is being renovated.
The banner was hung to call for "more financial commitment by the government to international climate protection," a statement on Greenpeace's German website said. "The climate crisis and the economic crisis can be solved together."
Deutsche Bank's towers "symbolise all the German banks that have received billions in financial support from the government," the statement said, even though the biggest German bank has not itself asked for aid.
Greenpeace climate specialist Karsten Smid said the time had come for massive investment in green technology. Such efforts could amount to an environmental "New Deal" - harking back to the economic programme implemented by US president Franklin D. Roosevelt to pull the United States out of the Great Depression.
The banner, 169 square meters (200 square yards) according to Greenpeace, was hung five floors from the top of the tower, around 140 metres (yards) above the heart of Germany's financial centre in Frankfurt.
Germany has created a banking sector stabilisation fund known as SoFFin, which has a total of €400 billion in guarantees and €80 billion in cash to support the crisis-hit banking sector.
"Greenpeace calculates that industrialised countries should provide at least €110 billion per year to effectively limit greenhouse gases worldwide," the statement said.