use &square; as placeholder
{% load static sekizai_tags %}{% spaceless %}
{% addtoblock "css" %}<link href="{{ stylesheet_url }}" rel="stylesheet" type="text/css" />{% endaddtoblock %}
-<i {{ instance.icon_font_class }}>{% if not instance.icon_font_class %}&blk12;{% endif %}</i>
+<i {{ instance.icon_font_class }}>{% if not instance.icon_font_class %} &square; {% endif %}</i>
{% endspaceless %}
\ No newline at end of file
