Board Thread:Wiki Discussion/@comment-26304798-20160805111610/@comment-26304798-20160806200249

The relevant templates are Template:Welcome and Template:Welcome anon for registered and anonymous users respectively. These templates are then inserted in MediaWiki:Welcome-message-wall-user and MediaWiki:Welcome-message-wall-anon.

The automated welcome message is signed by whichever admin was last active on the wiki.