Until today I have NEVER heard of this line.
I found this interesting and because I have had contractions alot this arvy and am due tomorrow so decided to go check myself out. To my surprise I do have the dark purple/red line and it goes all the way up. Im hoping it means something and I will have my lilman soon :D We will see.
I think its BS. Chances are, if you have a line its because its you've always had that line lol