Don't Speak by No Doubt.
It was the first time I actively listened to a sad song, and while I was only 4 or so, and couldn't really understand what the lyrics were about, I remember the emotion feeling so powerful. The radio station that played it went off air when I was 5, and I cried about it a lot. To this day I gravitate toward sad songs; there's just something about minor chords that I can't get enough of.
Yeah, I could see it being an issue for some less-common type of indicator, but everyone who drives knows what a blinker looks like. Nobody would mistake it for anything other than the right hand turn signal.
Hell, I wouldn't even notice the shape of the light; all you need to notice while driving is the presence of a flashing light on the right side of the vehicle - if you're looking intently enough to notice the shape of the light, you're not paying enough attention to everything else on the road.