There are a small number of weapons which can be reinforced to +5 with Dragon Scale. Most of the weapons come from severing the tail of a dragon.
Each of the five upgrade steps will increase the damage dealt by the weapon and in most cases, the scaling attribute will increase as well.
Weapon list

Shoot the tail of the Hellkite Wyvern for the Drake Sword, the first Dragon Weapon most players will have.
credit: From Software
Overview
- 10,000 Souls per upgrade.
- 10 Dragon Scales required to reach +5.
- Each reinforcement level will increase weapon damage
- Any Blacksmiths:Blacksmith or yourself (with a Weapon Smithbox) can reinforce.
Categories: Upgrading Dragon Weapon