I assume it's a request for you to show a little more care and respect for them. If that's the case, why don't they learn to USE THEIR BLOODY INDICATORS and show a little more care and respect for everyone else on the road?! I had two instances of sign-clad vehicles making turns in front of me without indicating in a single 5 minute trip today.
Seriously, this is one thing that irritates me more than most on the roads and yes, I know it's not just the baby carriers. Perhaps because I'm a biker I'm a little more sensitive about people trying to kill me by pulling out, turning etc without indicating, but even when I'm in my own car it drives me nuts.
Something should be built in to cars that prevents drivers turning the vehicle if the indicators aren't on. Could be a problem on bends, I suppose, but what the hell, it'd remove a few idiots from the roads.