Is there a name for these curved lines that represent head motion?
In comics, motion lines (also known as movement lines, action lines, speed lines, hites or zip ribbons) are the abstract lines that appear behind a moving object or person, parallel to its direction of movement, to make it appear as if it is moving quickly.
I can't find a corresponding (domain-specific?) definition of abstract lines as used above, but I'm guessing it's intended to imply lines which convey an abstract quality such as movement, emotion, etc. - rather than something "material", such as might be captured by a photographic image.
By implication therefore, exclamation marks or a lightbulb drawn above a cartoon character's head (indicating surprise, or a sudden inspiration) ought to also be called "abstract" lines / glyphs / punctuation marks, but I've never come across any such usage myself.
For anyone who thinks this is "Quiite Interesting" (such as me, now my attention is focused on it), I also found this post on Pinterest...
Hites, Vites, Dites, or Briffits.
Hites are horizontal lines to indicate speed or movement. Vites are vertical lines that add shine on a floor or an icy pond. Dites are diagonal lines to represent the reflection in a window or mirror. And Briffits are simply cloud-shaped dust clouds.
Fascinating stuff, domain-specific terminology.