All elements (sign up, catalog, invitation etc) can displayed or hidden by enabling or disabling the feature. When the feature is enabled, you can also control when online/mobile items are visible in the catalog.
The Online/Mobile feature must be enabled in order for the public to view ANY Online/Mobile element:
Go to Admin > Site Settings > Online/Mobile Bidding > Signup and Invitations
The Button Bar allows the public to filter/access items based on how bidsa re placed:
Go to Catalog > Preview Public View
Go to Admin > Site Settings > Catalog > Additional Online/Mobile Settings