In the Rich Text Editor (RTE)

This redirects every User to http://www.atlassian.com

This redirectes all users that is not member of "sales-users" to http://www.atlassian.com

In the Layout(s) for Global, Page, Blog post etc..

This redirects all requests to the Start page in the Public Space:

$helper.renderConfluenceMacro("{redirect:Public:Start|0}")

Placed in the Welcome Message:

{redirect:Public:Start|0}