The silver sword's inherent effect increases its damage by 20 points when used against undead enemies. Despite not being undead, werewolves and werebears are also affected.
The effect is not a normal enchantment, so it is affected by the Elemental Fury shout and silver swords may be enchanted at an arcane enchanter to stack with their inherent ability. The description "Especially effective against Undead" will remain. When a vampire, the sword does an additional 20 points damage. The silver sword cannot be crafted or upgraded at a grindstone. [Source: wikia]
You can download the papercraft model here: The Elder Scrolls V: Skyrim - Silver Sword Free Papercraft Download