Show message to user (or popup)

I am overriding the write method of the sale.order object. I want to inform the user of some things when the object is successfully saved (and I cannot raise an exception since it will roll back the write).

I tried returning something like

result = {'view_type' : 'form',
                'view_mode' : 'form',
                'view_id' : the_id_of_the_view,
                'res_model' : 'model_of_the_view',
                'type' : 'ir.actions.act_window',
                'target' : 'new',
                'context' : context,}

but still I cannot show any information to the user. I thought that it may be possible to call an action to display a view, something like wizards do, but cannot find any information or nothing.