The rallying cry emerged after a summer that saw the nation, once again, engaged in discussions about race, policing, and inequality. Instead of just taking to the streets after the deaths of black men at the hands of police and the subsequent murder of officers, protesters were urged — through hashtags like #bankblack and #blackdollarsmatter — to deposit $100 each into black-owned banks. And for Boston-based OneUnited Bank, the nation’s largest black-owned bank, the impact of the “Bank Black” movement was almost immediate. The bank, which has struggled in recent years, added more than $10 million in deposits in less than a month, said Teri Williams, the bank’s president.