how do people notice them?
They pop up on top of the "recent comments" list. Enough people read LW comments via this list (there are actually two, one for Main and one for Discussion).
In addition people get a notification when someone responds directly to a comment they made
I think it's past time for another Stupid Questions thread, so here we go.
This thread is for asking any questions that might seem obvious, tangential, silly or what-have-you. Please respect people trying to fix any ignorance they might have, rather than mocking that ignorance.