My own method used in list_display and value as boolean icon

Change your code to the following:

class MyClassAdmin(admin.ModelAdmin):

    list_display = ('my_own_method')

    def my_own_method(self, obj):
        if [condition]:       
            return True
        else: 
            return False
    my_own_method.boolean = True

which can be found in the documentation on list_display:

If the string given is a method of the model, ModelAdmin or a callable that returns True or False Django will display a pretty "on" or "off" icon if you give the method a boolean attribute whose value is True.