Each of these four phrases (listed in Steven Pinker (http://encyclopedia.thefreedictionary.com/Steven+Pinker)'s The Language Instinct (http://encyclopedia.thefreedictionary.com/The+Language+Instinct)) has a distinct meaning:

My sister's friend's investments (the investments belonging to a friend of my sister)
My sister's friends' investments (the investments belonging to several friends of my sister)
My sisters' friend's investments (the investments belonging to a friend of several of my sisters)
My sisters' friends' investments (the investments belonging to several friends of several of my sisters)
,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,, ,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,, ,,,,,,,,,,,,,,,,,,,,,,,,

Kingsley Amis, on being challenged to produce a sentence whose meaning depended on a possessive apostrophe, came up with:

Those things over there are my husband's. (Those things over there belong to my husband.)
Those things over there are my husbands'. (Those things over there belong to several husbands of mine.)
Those things over there are my husbands. (I'm married to those men over there.)[13] (http://encyclopedia.thefreedictionary.com/Apostrophe#cite_note-12)