"All you got to do is drop trou," she tells PEOPLE. "Pretty much that's the biggest statement you can make. Drop trou, get on a plastic horse and people start paying attention."
Johnston got naked (and got on a plastic horse) to bring awareness to the inhumane treatment of carriage horses in New York City. Four years after that memorable PETA campaign, the actress is being honored for her continued efforts to bring an end to the carriage horse rides that are a staple of the Big Apple by New Yorkers for Clean, Livable and Safe Streets (NYCLASS), an organization she was turned on to by a friend on the board.
"She asked me to go a screening of this movie Blinders. It's a documentary, a shocking documentary, about how the horses are treated and what really goes on in the horse carriage industry," she says. "It was something I never thought of. I guess I imagined they had a big paddock or a meadow somewhere to run in. The reality is obviously really stark and pretty horrible."
As a dog lover – Johnston is mom to a rescued pit bull named Pinky – the actress felt sympathetic towards the horses's plight, but she adds that animal lovers shouldn't be the only ones affected by this cause.
"I don't even really care about horses that much. I like them, but I'm not a horse person," she admits. "But it's so important; the issue is important. I don't even think you really need to be a horse lover to go, 'That's wrong. Something needs to change.'"