Decorative trim on a scarf?

[blarrg]

I am a very new beginner. I am working on a chunky scarf right now and I've been looking through some pictures of other scarves. I noticed that most of them have the finishing on the sides like in the attached picture. It just looks like a simple cleaner line on the side.
My scarf's sides don't look like that so I'm assumed that it's some kind of special finishing. I would like to have that look so I'm wondering how would I go about learning some more about that process.
Thanks!