Google is redesigning Sign-in page for Gmail, Google Docs and YouTube services, this is part of redesign of Google products with launch of Google+. If you land into Gmail homepage you’ll find a link at the bottom to preview Gmail’s new sign-in page. Once you click it, you’ll be switched to new sign-in page and it will become your default sign-in page across all Google products that currently have new design enabled.

Gmail new signin page

Switching back to Gmail’s old sign-in page

You can switch back to old page by clicking “Back to old page” option at the bottom. If you switch the browsers, the old page might come up again. These design changes shouldn’t affect your bookmarks,  they’ll work same as before at the same URL.

Gmail old signin page

Update : Gmail New sing-in page link