I misunderstood your title then. Double yolk eggs almost always need help hatching and even then you tend to lose one or the other.
They are often much larger, and longer than regular eggs. After you're used to seeing the normal size, you know by looking when you have a double on your hands.
I say that some of the sex links (comets, stars, etc) lay lots more double yolks because I'm always having friends ask me about the double yolk eggs they got at the grocery. Most of those would be laid by production breeds, which would be, by and large, sex link hybrids, and generally younger birds as well. One friend got jumbo eggs at Whole Foods, and all 12 were doubles!
You can make your own sex links from various breeds, but I think the hatcheries maintain specific production lines so that they hybrids will be super productive. You'll get a few doubles from almost any chicken, but get a few production girls from a hatchery and you'll probably get more.