I think he was asking after English verbs that are active in form, but passive in meaning. Latin has a whole slew of verbs that are passive in form but active in meaning. They are called deponent verbs: cf. amo 'I love' vs amor 'I am loved' with loquor 'I speak'. I'm not sure the first Dutch sentence is passive in meaning, but I'll take his word for it.

Ceci n'est pas un seing.