Confused....Still

ok so i've had tumblr for like a couple of months now and i still haven't really got the hang of it.

so आप know how आप reblog and then टिप्पणी दे on it,so आप link to your blog then put your टिप्पणी दे right?well everytime i do that i see that everyone else has this grayline going down right below their tumblr name...what is that या how do आप do that because everytime i टिप्पणी दे that grayline doesn't appear.. [example]

tumblrname:
[
[ < (grayline)
[
[
[lol omg wtf hahahaha forever reblog.
[
[