I agree with jaytea about the use of $highlight
this seems to work just as long you have the nicks added in ur highlight list

on *:text:*:#:$highcheck($1-)
on *:action:*:#:$highcheck($1-)
alias -l highcheck { 
  if ($highlight($1- $lf) && !$($+(%,f,$wildsite),2)) {
    inc -u15 $+(%,f,$wildsite)
    noop $tip(Highlight,Nick Highlight,$nick highlighted you$&
      in a $event message in channel # Saying: $crlf $1-,15)
  }
}

Or use the highlight dialog mirc provides an set up a tip message from there.