It has their signature, to prevent others from stealing it (which I should start doing)

But what i mean is that they draw on the sticky note

I think I need visual example to get what you are saying. Do you have one? Or something similar to it?

No I don't have any saved examples. It's just something I've noticed pop up once in a while, while scrolling through tumblr.

do you mean something like this? http://anime-master-96.deviantart.com/art/Sketching-on-the-train-Sticky-Notes-D-393243470

No (although that's amazing) like they have the art on paper and then on the paper there is a sticky note with the rest of the picture on it

*After further digging through the web*
I found this first: http://www.online-instagram.com/media/1085110800635081938_1599104812
Then came this one: https://s-media-cache-ak0.pinimg.com/236x/c5/60/38/c56038aa7bf8059d4b9fd1bd4f25b39c.jpg
And finally, if I interpreted your description correctly, I might have found the origin of it all: http://www.piecesbypolly.com/2013/12/sticky-note-art-and-simple-stocking.html
.
NOW, is /that/ what you meant?

YES,, although it is mostly done with original art

Well, the last one was done by a kiddie, maybe they were trying to teach him something.
It does bring some other feeling to the drawing, though, I can't really tell what reasoning the others had when continuing their drawing on a sticky note.
It's an interesting concept; certainly different.

To stop smudging, because sometimes while shading at an angle, you might smudge some lines etc

I think that's something else, though. You are not using the sticky note as a support for your hand to avoid directly touching the drawing; you ARE continuing a drawing on the sticky note.

Oh...