For Pro publishers with their custom header set to ON
If you have turned your custom header to ON, you have hidden the Paper.li Main Menu icon (upper left) from your readers.
Desktop: click ESC on your keyboard to sign-in and the menus will be visible again.
Tablet or mobile: If you are editing your paper via a mobile device, add /signin to the end of your paper URL and bookmark the URL for easier access.
Please note: different devices render different results. It's possible that on tablets or phones you may need to add http:// in front of the URL (if your browser doesn't do it for you) for the sign-in to work.