My husband has being served a WRIT in his mailbox with a answer date for possession of personal property (a vehicle). Does he have to acknowledge the served document since he is away and it was served directly to him? Is this a legal served or should it be through registered mail or in person? What will happened if he don't respond?

-Confused

Each state has its own rules, regular mail or being put on the door of the home is very proper in some places.

Not sure, you said it was served directly too him ? Then that would be service.

So what is happening, normally on a auto, they merely just repo it without telling you anything

Service by mail is legal for certain court actions. If he hides that he received the summons it only delays the inevitable. And if he ignores it, you will probably have a default judgement entered against him. .