My problem is similar to this thread: Can "list_display" in a Django ModelAdmin display attributes of ForeignKey fields?. I want to display a foreign key attribute from the list display. This attribute is a BooleanField. Normally, it would display a check or cross if the admin page is on the model itself containing the field. Such as this:
However when I reference this to other admin page.
class ProofOfPaymentAdmin(admin.ModelAdmin):
    list_display = ('id', 'reference_number', 'user', 'is_subscribed',)
    def is_subscribed(self, obj):
        return obj.user.is_subscribed
The return from the list display is the boolean values True or False.
How can I change this to display the icons check or cross similar from the above?
Update 1: Result from first answer:



 
    