Highlight (¿) in text mode

I see no other way than to make < and > active so they print something evident when used in text mode and the standard symbols in math mode. Of course any < or > comparison in the context of ifnum (or derived) that are not buried in macros defined in the preamble will die horribly.

documentclass{article}

AtBeginDocument{%
  begingrouplccode`~=`< lowercase{endgroupprotecteddef~}{ifmmode<else OUCH!`fi}%
  begingrouplccode`~=`> lowercase{endgroupprotecteddef~}{ifmmode>else OUCH?`fi}%
  catcode`>=active
  catcode`<=active
}

begin{document}

$a<b$ $a>b$

<>

$left<xright>$

end{document}