¯_(ツ)_/¯
EDIT:
I can only shrug at the shrugging thing not rendering properly.
The backslash is used to indicate that the following symbol, which is otherwise used for formatting, should to be displayed. For example sigh vs. *sigh*
For this reason, a single backslash is not displayed and you have to use two consecutive backslashes.
¯\(ツ)/¯
EDIT: for some reason, you have to use three backslashes.
¯\_(ツ)_/¯
Two backslashes escapes the first backslash but not the underscore. Three escape the backslash and the underscore.