In speech, the context will supply the meaning. If the person to whom you are speaking doesn't know if there is more than one owner/attorney/nurse, then you have to tell him explicitly.

In writing you have less knowledge of the reader, so you have to indicate with the punctuation.

Having said that, I'd like to point out that in some cases the context makes it obvious. For instance, a car is considered to belong exclusively (or primarily) to one person - each manual is for one owner of one car, so it's an owner's manual.

The question is whether the thing is directed or meant for one person at a time. In some cases either the plural or singular form would be quite okay. Nurses' notes for any and all nurses; nurse's notes if you want to think of each nurse consulting them one at a time.


Cheers

John.