-Have people choose a "family name" when they create their first character. From now on, all the characters of the account share the same surname.
-Family Names are unique. In normal conditions, no other account can have the same family name.
-Either make surnames visibile if the person is kinned or via an npc (civil registry anyone?) by paying a fee.
Why do this? Two reasons. One is that this would stop scamming via making appositely named alts. It had no sense anyway. Sure, one may pretend to be another person, but that would work just until one finds the surname.
The second one is due of lore. Since the other character can inherit from a dead person, one should suppose they're from the same family. If marriages were to be introduced, subsequent chars by the couple may also choose which one of the two family names to use. Drama wise, feuds between families could be created this way.
There may also be some other way to share the same surname (it would be done before you choose a surname, obviously) but that would have to require some kind of confirmation given by the rightful owner of the family name. Doing so would avoid the scamming explained above.
So, in the end, it could be not that useful, but a nice addition lore wise.