///

In Japanese, ///, three slashes or more, may mean someone is blushing, red-faced, probably embarassed. For example:

• minaide///
  見ないで／／／
  Don't look [at me]. *blushes*

Naturally, this originates in the parallel diagonal lines used in manga to render blushes. See blushing lines for details.

Anime: Gekkan Shoujo Nozaki-kun 月刊少女野崎くん (Episode 1)

These slashes may also appear in manga text balloons when the character that is talking isn't visible in the panel where their text balloon appears.