Marker on my screen

So, some of the stories here are really long and I can't read them in one setting, so I have been using a marker to mark the position of the slide thingie before I shut down for the night. Before you all laugh at me, how else can I do it? It is really troublesome to find my place again when I come back on line.

I am worried about getting the marks off my screen.

Is there some sort of book mark thingie I can use so I can come back to the right place?

Thank you.

Gwendolyn