nobreak-char-display

nobreak-char-display is a variable defined in `C source code'.
Its value is

t

Documentation:
Control highlighting of non-ASCII space and hyphen chars.
If the value is t, Emacs highlights non-ASCII chars which have the
same appearance as an ASCII space or hyphen, using the `nobreak-space'
or `escape-glyph' face respectively.

U+00A0 (no-break space), U+00AD (soft hyphen), U+2010 (hyphen), and
U+2011 (non-breaking hyphen) are affected.

Any other non-nil value means to display these characters as a escape
glyph followed by an ordinary space or hyphen.

A value of nil means no special handling of these characters.