Laughter Manga Symbol - Crossed, Segmented Lines

In manga and anime, a segmented arc crossed by perpendicular lines drawn over a character's head means they're having fun, laughing, or just being cheerful and lively in general.

In Japanese, these are called niko-sen ニコ線, "smile lines."^{(tonbi.jp:ニコ線)}

Character: Hiraga Saito 平賀才人
Anime: The Familiar of Zero, Zero no Tsukaima ゼロの使い魔 (Episode 3)

• Examples
• References

Examples

For reference, some examples:

Manga: Yotsuba to! よつばと！ (Chapter 8, よつばとおえかき)

• Context: Yotsuba よつば has fun drawing.
• tanoshii
  楽しい
  Entertaining. Fun.

Character: Yoshida Yuuko 吉田優子, Shamiko シャミ子
Anime: Machikado Mazoku まちカドまぞく (Episode 1)

Left: Henry Maaka, ヘンリー・マーカー
Middle: Carrera Maaka, カレラ・マーカー
Right: Maaka Ren 真紅煉
Anime: Karin かりん (Episode 7)

Left: Excel エクセル
Right: Pedro ペドロ
Anime: Excel♥Saga, エクセル♥サーガ (Episode 1)

• gayagaya
  ガヤガヤ
  For a group of people to be noisy by talking loudly. For example, for a classroom to be noisy because the students are talking to each other loudly.
  (mimetic word)
  • urusai
    煩い
    Loud. Noisy. Annoying.
• geragera
  ゲラゲラ
  Laughing heartily.

References

• ニコ線 - tonbi.jp, accessed 2020-03-28.