Facebook has just announced a change to Pages that will make it clear to admins which other admins posted certain content on the page's behalf. The changes are set to go into effect on February 20th and will not be retroactive.
"Starting on February 20, the names of admins will show next to their posts and comments. This will be visible to anyone with an admin role on your Page," says Facebook in a pop-up post at the top of pages.
Here's a little bit of additional clarification from Facebook:
On a Page post, the name of the person who posted will be listed below the name of your Page next to Posted by. On a Page comment, the name of the person who commented will be listed below the comment next to Commented on by. Keep in mind that only people who help manage your Page can see this information.
This info will also appear in your page's activity log, where you'll be able to see who has scheduled posts.