World Marker

Not to be confused with Raid target icons.

click the tiny yellow triangle on the left edge of your screen

click the flag icon in the bottom right of the raid control panel

select which color beacon to place

all superbears report to the blue square and shake your bootie

Raid Beacons are used by raid leaders to mark locations on the battlefield. They appear as a cylinder of colored light topped by a symbol that players will recognize from the Raid target icons set. Unlike Raid target icons, Raid Beacons are not available to individual players or 5-man parties. They are only available during a raid.

Beacons can only be placed by the raid leader or raid assistants. Players using the default raid interface must open up the pop-out raid settings panel and look for the flag icon. Clicking that button pops up a menu of symbols. Selecting a symbol activates a tiny AoE symbol on the player's cursor that enables him to target a section of floor and click to place the beacon.

Beacons are usually used to designate places for specific groups or players to stand, or where to place a monster.

Some raid target icons do not have a corresponding beacon.

macros and add-ons

A macro from MMO-champion forums (untested):

/click CompactRaidFrameManagerDisplayFrameLeaderOptionsRaidWorldMarkerButton
/click DropDownList1Button1

1 is blue; 2 is green; 3 is purple; 4 is red; 5 is yellow; 6 is cancel all flares.

Add-ons include "Raid Flare Key Binding", "Smoker", and "OPie World Markers", although they all date from late 2010.

Notes

Use of the Raid Beacons can sometimes trigger an add-on data tainting error dialog (and prevent the player from placing any beacons). It might be a flaw in Blizzard's data tainting system, or it could be bad behavior by widely-used add-ons. If /reloadui does not solve the problem, promote someone else in the raid to assistant and have them place the beacons.

Patch changes

Patch 4.0.3 (2010-11-16): I think this is when Blizzard added raid beacons to the game