Even if you don’t know who Dave Loewenstein is, it’s highly likely that you’ve come across his murals, which often stretch the length of the walls of Lawrence parks, schools, buildings, passageways and elsewhere. In 2017, Loewenstein, responding to a call to action from the U.S. Department of Arts and Culture, which is not a federal agency but a “loose collective,” as he describes it, created a series of three postcards inspired by Martin Luther King Jr.’s antiwar speech, “Beyond Vietnam: A Time to Break Silence."