Also called single knotted line stitch, scroll stitch makes an attractive border. And marking a line on your fabric will help to keep your line straight when you work this stitch.
First bring your thread to the front. Make a loop with your thread to the right and in a clockwise direction.
Take a tiny stitch from from top to bottom beginning slightly above the marked line and coming up on the line itself. Make sure that the looped thread lays under both ends of the needle.
Pull the thread firmly so the loop tightens around the needle.
Then pull the thread through to complete your first stitch. You'll know immediately if you've done it wrong because there will be no loop holding the thread inside. If that happens (and it happened to me several times so don't worry) just undo that stitch and begin again.
Loop the thread to the right again and repeat.
And continue working your stitches in the same way until you've completed your line.
This would be good for waves, wouldn't it?