When you search for videos online of plucking a string on an instrument such as the guitar, a surprising number of searches lead you to videos such as the following:
This is not how plucked strings look like! And they don’t have anything to do with Harmonics either! The reason why you are seeing those shapes on the guitar is due to the rolling shutter effect on your camera.
But if you do want to see how plucked strings look like, the following videos would be your best bet:
Links:
DIY: Tutorial running you through how you can recreate the effect on a guitar for yourself