I think signature should be visible on all pages but the main namespace. Currently it's only available on talk pages but there are many places (e.g. Wikipedia:Village pump) in the Wikipedia namespace where you have to leave your signature.

A quick fix if anyone would want it (we have this on pl.wiki):
if (
typeof(editToolbarConfiguration)=="object"
&& typeof(editToolbarConfiguration.main.groups.insert.tools.signature.filters) == 'object'
&& editToolbarConfiguration.main.groups.insert.tools.signature.filters[0] == 'body.ns-talk'
)
{
editToolbarConfiguration.main.groups.insert.tools['signature_non_talk'] =
{

		labelMsg: 'edittoolbar-tool-signature-nt',
		filters: [ 'body.ns-4' ],
		type: 'button',
		icon: 'insert-signature.png',
		action: {
			type: 'encapsulate',
			options: {
				post: "--~~~~"
			}
		}

}
}

Version: unspecified
Severity: enhancement