Damage Amplifier

The Damage Amplifier (just Amplifier, or UDamage due to its shape) is a power-up that temporarily enhances the player's weapon damage. It also makes a distinctive sound when picked up, and every time the user's weapon fires to alert others that someone is using it. It is much sought after in multiplayer games due to its relatively big impact.

The original Unreal design resembled a car battery, but starting with UT it became U-shaped, possibly inspired by Unreal's "U" logo, and the Skaarj blades through that. Originally gold in UT, purple became the item's telltale color in later games.

Unreal
In Unreal the Amplifier resembles a battery and only enhances energy weapons: the Dispersion Pistol and ASMD.

Unreal Tournament
The Damage Amplifier looks like a spinning, gold symbol, the same symbol used by the green team in multiplayer games.

Players carrying it have a purple glowing weapon.

Unreal Tournament 2003 and 2004
UT2003 and UT2004's Double Damage pickup resembles that of UT, but is purple and semi-transparent. It looks somewhat like a hologram. Players carrying it glow purple as well.

Unreal Tournament 3
UT3's Damage Amplifier is purple but has a more technical look with added metal bits, similar to the UC2 version. Another player can use his/her Impact Hammer's alternate fire to knock it away, to pick up and use for the amount of time still remaining. Combined with Berserk or Invulnerability it gives the user a "Juggernaut" award.

Unreal Championship
UC's Damage Amplifier is similar to that of UT2003.

Unreal Championship 2
In UC2 the amplifier is referred to as "UDamage" (Unreal Damage). It is purple, but has a somewhat more technical look with metal bits. If a player picks it up, it spawns a slowly growing, transparant, purple animation of that player looking like (s)he is roaring, clearly indicating the item was picked to other players. This can be seen roughly two thirds into this video.