JSFiddle - React, Tailwind, and code Playground

HTML

<input type="text" name="address" value="POB123"><br>
<input type="text" name="address" value="P.O.B.123"><br>
<input type="text" name="address" value="POB 123"><br>
<input type="text" name="address" value="P.O.B. 123"><br>
<input type="text" name="address" value="PO Box 123"><br>
<input type="text" name="address" value="P.O. Box 123"><br>
<input type="text" name="address" value="P O Box 123"><br>
<input type="text" name="address" value="P. O. Box 123"><br>
<input type="text" name="address" value="P OBox 123"><br>
<input type="text" name="address" value="POBox 123"><br>
<input type="text" name="address" value="PoB#123"><br>
<input type="text" name="address" value="POb #123"><br>
<input type="text" name="address" value="po Box #123"><br>
<input type="text" name="address" value="POBox #123"><br>
<input type="text" name="address" value="Box123"><br>
<input type="text" name="address" value="Box 123"><br>
<input type="text" name="address" value="Box #123"><br>
<input type="text" name="address" value="123 Box Street"><br>
<input type="text" name="address" value="123 Poor Box Road"><br>
<input type="text" name="address" value="123 Harpo Box Way"><br>

CSS

span.pob {
    color: #F00;
    font-weight: bold;
}
input { margin: 2px; }

JavaScript

$('input[name=address]').each(function() {
    var pattern = new RegExp('[PO.]*\\s?B(ox)?.*\\d+', 'i');
    if ($(this).val().match(pattern)) {
        $(this).after('<span class="pob">No PO Boxes</span>');
    }
});