Manual:User signatures

Users can sign their comments using the wikitext  and some other variants; Help:Signatures explains this in more detail. The signature code is replaced by an actual signature during the pre-save transforms.

Customization
A number of system messages can be used to customize signatures in some context or another:
 * MediaWiki:Signature (doc): the default signature format for logged-in users. Can be overridden via the  user preference. Must follow some rules. A timestamp will be appended to it.
 * MediaWiki:Signature-anon (doc): the signature format for anonymous users.
 * MediaWiki:Sig-text (doc): customize the wikitext inserted by the signature button on the MediaWiki editing toolbar.
 * MediaWiki:Discussiontools-signature-prefix (doc): customize the wikitext of the signature appended by the DiscussionTools extension.

Most editing tools provide a button for adding a signature; this is usually limited to talk namespaces. Most editing tools respect which can be used to enable signature buttons on some non-talk namespaces as well. (The signature wikicode itself works in all namespaces.) Some tools also enable the signature button on pages with the  magic word.