From Team Fortress Wiki
The Name Tag is a tool item, represented as a blank tag bound by a string.
Using this tool in conjunction with a compatible item in the backpack allows the player to bestow a customized name (of 40 or fewer characters) upon that item. Using a Name Tag with an item that has already been given a custom name will rename the item. Name Tags are consumable items, and may only be used once. A named item can be reverted to its original state by selecting the item in the backpack and pressing the 'Restore' button. Restoring an item will remove all customization from it, including custom names, descriptions, and paint. Restoring an item to its original state will not refund the Name Tag.
Renaming an item will preserve the item quality whilst placing quotation marks around the new name. Any prefixes such as "The", "Vintage", "Strange" or "Unusual" will be overwritten. This includes craft numbers. In order to preserve the same style as unmodified items, title case should be used, such as capitalization of the initial letter of each word. When a Name Tag is used on a Strange weapon, the weapon will display its kill count and rank above the description.
If a stock item is renamed, it becomes a Unique item and the player will subsequently find it as an item drop. The newly named item will exist separate to the original stock item. The player can then choose which item to equip through the character loadout menu. If the name of a stock weapon is reverted, the weapon will remain in the player's inventory. As of the Über Update, re-named/described Stock weapons can be used to make scrap metal.
- Added Name Tag to the game.
- Named items can be now be reverted back to their default name.
- Purchased Name Tags are now tradable.
- Edited item names and descriptions that contained grave accents (’) to use single quotation marks (').
- [Undocumented] Grenade Launchers, Pistols, and Shotguns using Name or Description Tags now properly use the c_model equivalent.
- [Undocumented] Fixed Engineer's first-person arms using the wrong bodygroup when having a renamed Shotgun or Pistol equipped with the Gunslinger.
- Using a Name Tag while in game notifies everyone of the name change.
- [Undocumented] Lowered the price of Name Tags.
- Name Tags are now included in Class Starter bundles purchased from the Mann Co. Store, replacing a class specific hat.
- Renamed items do not properly appear on disguised Spies. For instance, if a Spy disguises as a Medic wielding a renamed Medi Gun, the customized name will not show up on the disguise when an enemy looks at them.
- Name Tags used on weapons that became vintage following the March 15, 2011 Patch cannot be removed.
- Community items with a Normal variant that were received before name tags were introduced cannot be named.
- Name Tag cannot be used on Craft items like Reclaimed Metal, any edition of Mann Co. Supply Crates, Dueling Badges, Noise Makers, Strange Parts, weapons being used on a test run from the Mann Co. Store, all four Tour of Duty Badges, Dueling Mini-Games, other Name Tags, Stock Disguise Kits, Stock Destruction PDAs, nor Mann Co. Supply Crate Keys.