The signs were supposed to tell emergency services that there was a kid in the car if the driver was knocked out and it wasn’t immediately obvious. I guess with seatbelts, isofix and better car seats, people don’t get thrown out the car in a crash like they used to so the signs don’t add very much.
When I did my motorcycle test, the the instructor was quick to point out that the signs were really valuable as it pointed out people who were likely to not be paying attention to the road. He wasn’t wrong either.
Back to the OP. My Mrs didn’t want tinted windows either as she felt it was too dark in the car and she couldn’t see properly when it was dark.