henohenomoheji へのへのもへじ

In Japanese, henohenomoheji へのへのもへじ refers to a face drawn using the hiragana characters he へ for eyebrows and mouth, no の for eyes, mo も for nose, and ji じ for outline, though this last ji じ is often omitted.

It's also called hehenonomoheji へへののもへじ.

Character: Moegi Emo 萌黄えも
Anime: Kiratto Pri☆chan, キラッとプリ☆チャン (Season 2) (Episode 20)

Examples

For reference, some examples of henohenomoheji:

A face drawn using the henohenomoheji へのへのもへじ characters.

Source: wikimedia.org (Public Domain)

Anime: En'en no Shouboutai 炎炎ノ消防隊 (Episode 24)

Sakuragi Hinako 桜木ひな子, transformed into a scarecrow.

Character: Sakuragi Hinako 桜木ひな子
Anime: Hinako Note, ひなこのーと (Episode 1)

kakashi
案山子
Scarecrow.

A teruteru bouzu てるてる坊主 with a henohenomoheji へのへのもへじ face

Anime: Toradora! とらドラ！ (Episode 8)

teruteru bouzu
てるてる坊主
A charm used to control the rain.

Background characters with eyes shaped like the の character.

Anime: Suzumiya Haruhi no Yuuutsu 涼宮ハルヒの憂鬱 (Episode 射手座の日)

mobu kyara
モブキャラ
Mob character. Background character.

Manga: Mahoujin Guruguru 魔法陣グルグル (Chapter 4, ジェム平原)

Context: Kukuri ククリ correctly drew a "magic circle," mahoujin 魔法陣, but only after countless failures. She shows the failed magic circles to Nike ニケ.
hora
ほら
See.
...
sappari sappari
さっぱりさっぱり
(in this series, the sappari fairy is summoned whenever something silly happens.)
- sappari
  さっぱり
  Completely. Specially in the sense of completely clean. (mimetic word.)
  (typically used as an abbreviation of)
- sappari wakaranai
  さっぱりわからない
  To completely not know.
  To have absolutely no idea.
shippai
しっぱい
Failure.

By the way, sometimes characters' eyes are drawn like the no の character due to the iris being at the corner of the eye. This may get called nonojinome 「の」の字の目.