There's something interesting about these cards - they're helping DEFCON people adopt a usable vocabulary for talking about harassment, an addition to our jargon.
Here's an example. A few days ago I was part of a Rio elevator full of DEFCON people when it stopped at a floor where a non-attendee woman was looking to get in. There was obviously no room inside, but one of the guys hollered at her to "get in anyway - you're a cute woman - we love women - this ratio needs to be improved!" She instantly disappeared. As the elevator door closed, another guy looked at him and said "dude, yellow card." Silence the rest of the way down.
It's a small thing, but I was the one DEFCON woman in the elevator, and I appreciated that verbal yellow card - in other words, while I was in the middle of mentally processing what had just happened and whether creepy attention would shift to me, a fellow attendee had quickly and effectively reset the tone of the elevator to basic civility. This is good.