Sign

Signs are non-solid blocks that can display text.

Obtaining
Signs can be broken with any tool, or without a tool, but an axe is fastest.

A sign will also break and drop itself as an item if the block the sign is attached to is moved, removed, or destroyed.

If a sign is broken while being edited, the player will /will not continue to edit the sign.

Natural generation
An oak sign can be found in igloo basements.

Spruce signs generate in some taiga village houses.

Spruce signs can be found inside taiga village house chests.

Usage
Signs can be used to display text.

Placement
Signs may be placed on the top or side of other blocks (including some non-solid blocks like fences, glass, and other signs). To place a sign, a sign item while pointing at the block the sign should be attached to, enter the desired text (possibly none), and click the "Done" button or press "escape" on a keyboard (or press × in Bedrock Edition,  in an Xbox controller,  in a PlayStation controller). To place a sign on a block that can be interacted with by the control (for example, chests, note blocks, etc.),  while placing the sign.

Signs placed on the top of a block stand on a short post and will face in the direction of the player who placed it, in any of 16 different directions. Signs placed on the side of a block simply float there, even if the block doesn't make contact with the sign.

Text
When entering text, four lines of text are available. To switch between lines, the player can press Enter or the up/down arrow keys. The line which is currently selected will have a greater-than (>) at the beginning and a less-than sign (<) at the end.

While editing, typing and backspacing occur only at the end of a line. It is impossible to insert text in the middle of an already typed line - the player must delete and re-enter text in order to make edits.

After the editing window is closed, the sign's text can only be changed by removing and replacing it, removing the text in the process. Copy and Paste cannot be performed, and no more than the basic/shifted characters on a keyboard may be entered. The Xbox 360 Edition and Bedrock Edition supports both the on-screen keyboard and direct editing of text using a USB keyboard or controller chatpad.

The combination +  can be used to copy an already-placed sign and place it down again with the same text shown as the original.

Colored text can be applied to signs in survival or creative mode by pressing on a sign (with text on it) with any color dye.

With a map editor, the color of sign text can be changed with formatting codes.

Signs can be created with JSON text which allows complex formatting (colors, bold, italic, etc.), hover and click events, localized translation (for Minecraft technical terms, like "Redstone Repeater", otherwise translations must be provided in language files in resource packs), and the incorporation of scoreboard values into text. Use the command to create or alter JSON signs.


 * Example:

Signs can post the success count of JSON text hover and click events to scoreboard objectives. The objectives to be used can be specified by running the command or by modifying the sign's NBT data directly with the  command.

The text color can be changed by right clicking with dye.

The text displayed on a sign will not be affected by lighting.

Interaction
Signs act as though they have a action, so the player is unable to place blocks or use items while the cursor is pointed at them without.

Signs will be removed and drop as an item when pushed by a piston (trying to pull them does nothing), except in Java Edition, where a sign will cause the piston to not extend.

Signs have no collision mask (they are completely non-solid), so items and mobs can move through sign blocks. Other blocks (including other signs) can be placed on any edge of a sign.

Water and lava will flow around signs. Lava can create fire in air blocks next to signs as if the signs were flammable, but the signs will not burn up (and can't be burned by other methods either, except in Bedrock Edition).

Fuel
Signs can be used as a fuel in furnaces, smelting 1 item per sign.

Collecting cacti
When attempting to place a sign on a cactus, the cactus will break and the sign will drop as an item.

When attempting to place a sign on a cactus, the cactus will break and the sign will drop as an item after the menu is closed.

Breaking double tall grass
When replacing the top half of tall grass, the grass will break and the sign will drop as an item.

Block data
In Bedrock Edition, a sign's block data specifies the direction it is facing.

Block entity
A sign has a block entity associated with it that holds additional data about the block. The block's block entity ID is.

Video
Note: This video is outdated, since signs in different wood types were added in 1.14 snapshot 18w43a.

Trivia

 * If a sign is placed within a ring of four cacti, only certain cacti will break, depending on the direction.