Bukkit

/command
        - Runs a command from the player who clicked the sign.

/*command
        - Runs command with elevated permissions using the '*' node.
        - Does not work for OP commands like /stop.
        - (For WorldEdit //wand, use /*/wand).

/^command
        - Runs command as op.
        - Cannot use this to op the player, as they are simply deop'd.

/#command
        - Runs command as console.
        - Plugins won't get the player, so they can't do any specific player processing.

-
        - End a restriction.

@group
        - Limits the sign use to only that group.

~seconds
        - Adds a per-player cool-down on the sign. The sign cannot be used again until this cooldown expires.

$amount
        - Adds a charge to use a sign (Economy).

&node
        - Require a permission node to use the sign.

!
        - Restriction is inverted beyond this point (acts as an 'else' statement)

?condition
        - Make a conditional check optional - displays no error if condition is not met.
        - Condition can be any of the conditions above (like @group).
        - v1.7.9+ ONLY.

!condition
        - Invert/negate a conditional check.
        - !~5 will only allow the commands to be run if the sign is clicked twice within 5 seconds.
        - Condition can be any of the conditions above (like @group).

\message
        - Print the message to the player chat

.message
        - Print the message to chat as the player
        - v1.8.0+ ONLY.

%seconds
        - Delay the sign's execution by the set interval
        - Does not lag server

`seconds
        - Pause execution of a CommandSign for a random amount of time.
        - v1.8.0+ ONLY.

@group1,group2,group3
&perm1,perm2
        - Allow multiple groups to pass the restriction block
        - v1.8.3+ ONLY