Some thoughts:
Even with people you have a solid, positive relationship with, one-on-one talks about child safety are difficult. I don't know if it's easier or harder with strangers. I think most people respond better to messages that can't be read as personal (i.e., PTO newsletter, school-wide initiative, newspaper article, letter to the editor), and that don't assume the caregiver should have known this information.
Still, because car seat safety is a life or death issue, in a one-shot opportunity, I will shamelessly appeal to what I believe to be the best or the worst in the person I'm talking with (guilt, fear, pride, leadership, perfectionism, etc), but it's my least favorite way of approaching people, and I doubt it's all that effective. Unfortunately, it's usually seeing some awful situation that prompts my desire to educate someone, and that's often the situation when a person will be most defensive.
Offering information as something brand new to you (e.g. "I just heard the AAP is endorsing rear-facing as long as possible") takes away some of the sting that people sometimes feel when they've been personally singled out. As a grandmother, I can truthfully tell people that I am amazed at how much things have changed since I was a mother of young children, adding, "for example, I had no idea that pediatricians are recommending . .," or, "I went to a car seat tech to get this checked, b/c there's so much to consider now," or "Have you seen this web-site? I learned so much from it." I think that puts me on a more equal footing, so it's more like the two of us looking together at information from "experts."
No matter how well you do it, I think it's just hard to establish your own credibility with people when so many people they know are doing it just like they do. The natural response is to marginalize the one doing it differently (the car seat fanatic, or the health food nut). It's so much easier when there's a critical mass of support. I'm not sure how to get that, other than finding a way to address the group, or finding someone who is highly regarded by that group and getting them to take the lead. I'm guessing this happens a lot in some communities where techs are active, and not at all in others.
Is it completely ridiculous to think about doing something like a walk for child safety? Maybe in Detroit? (Is already happening?) Walks for breast cancer, AIDS, etc. raise tons of money this way, but the main benefit is how the grassroots method (each walker approaching many others for donations) exponentially builds awareness in a much larger group. The trick would be staying away from blame and guilt to a focus on what people don't know that could save their children's lives. (The people who do know and don't care wouldn't be touched in any event, so there's no point in worrying about them.) Money raised could be used for public education, including simple mnemonics that could help people remember all that has to be remembered to keep their children safe.
To me, simplifying the complexity is absolutely critical. I honestly don't know how busy parents sort out and keep track of all they need to know and remember regarding child safety in cars. It's not just one installation - it's every time you take it out and put it back in, every time you put your child in, when you change the RF to FF, when the child grows, when winter comes, when you buy a new car, or use someone else's car, when your car seat passes its expiry date, when you have an accident, when you travel, when you have more kids and need to buy a new seat, or change how they are configured in the car, when you have loose objects in the car, etc, etc. I kind of enjoy learning all this and knowing I'm doing a good job, but for most people, I imagine it's just an important chore, and the more easily and quickly it can be done, the better. Right now, it's not easy and it's usually not quick to really learn how to safely secure your child.