All I can tell you is that if you are going to undertake this endeavor, you should get extremely well-versed on the subject of "libel" (which is defamation in the written form [and I imagine a billboard would constitute the written form]) as you don't want to open yourself to any lawsuits from Crailtap or the individuals themselves.
People with attys and money behind them can be extremely litigious and, sadly, with libel, it's not necessarily what is true but what you can prove (which sucks for victims trying to speak out).
I only say this to look out for you.
Do some research on the allegations against Harvey Weinstein and Brett Rattner and the legal actions those women who wrote about their experiences with them faced.
I would suggest a safer (legally) for you approach would be to try to organize a boycott with suppliers, distributors and ultimately consumers, wherein you try to leverage the free market to achieve your goal.
I would start with a letter-writing campaign that carefully documents the allegations, and the company's responses (or lack thereof) to said allegations.
I would suggest that if and when you craft these letters, you highlight that these folks have not been convicted of any crimes and you are not speaking on their guilt (which I can imagine sucks if you have had a personal experience with one of these individuals you know to be true) only that the allegations exist and they're troubling.
Remember: unfortunately, it's not necessarily what happened, but what you can prove.
Again, I say all this to look out for you, and I hope that you can take the necessary precautions to protect yourself legally because you know these folks are not going down without a fight and it would be horrible to suffer legal/financial ramifications (in addition to whatever health and mental suffering you have already expreienced at the hands of someone) just for speaking out, if you don't do so smartly with the utmost care for the rules of the law. Good luck.