The Signal Insight Maria Black, only the seventh CEO in ADP’s 77-year history, often lingers before her predecessors’ portraits on the walk to her office. They’re a reminder of how ADP’s former leaders navigated previous moments of disruption, from financial crises to the dot-com bust. And when she’s facing a particularly tough conundrum, she says, “I go look at the oil paintings.”Black, the self-styled historian of the $110 billion, 67,000-pers…