We need to get the button for signatures enabled in two non-talk namespaces because they're meant to let people comment to make requests, report problems etc. (such as it happens in Wikipedia's Help desk); the ability to easily sign is a must because most people won't bother copy/pasting the tildes and will leave unsigned messages.
The namespaces are Nonciclopedia (4) and Aiuto (12). The other namespaces are fine as is. In case it might come in handy to you, someone on MediaWiki told me it's made by editing $wgExtraSignatureNames