Unfortunately, escaping wildcard characters with their $chr() equivalents won't work, as mIRC will still treat them as wildcards when making a wildmatch comparison. In order to check for them in a string, you'll need to use them in a context where they are
not treated as wildcard characters.
In your particular case, since you already appear to be checking if the string occurs anywhere in the line, regardless of what's around it, the
isin operator may be a good choice:
if (*** isin $1-) { ... }
You could also use regex if you want the matching requirements to be highly flexible. (Just keep in mind that you'll need to escape the * and ? characters (in the regex sense) so that they are not treated as meta characters:
if ($regex($1-,\Q***\E)) { ... }
; or for an example showing more flexibility...
if ($regex($1-,\b\Q***\E\b)) { ... }
There are, of course, also things like $istok() and == for checking whether such chacters are in (or make up) the string; it all depends on your particular need.