As you know, you can customize the logon sign-in pages with your company logo, custom image and color (this requires to have at least an Azure AD P1 license).
Well, the Company Branding has been updated and you can now add hyperlinks and add simple formatting like bold, underlining or italics.
To start customizing your company branding to use this new capabilities (or even start using the Company Branding) logon to your Azure portal (https://portal.azure.com/) or Azure AD portal (https://aad.portal.azure.com/) and go to the Azure AD blade
There open the Company Branding blade
Then edit the existing branding (if you have added additional language you will need to edit them too)
Then in fields where you can add text use the following syntax to use the basic formatting or hyperlink options:
If you want to write a return carriage you need to hit Enter twice
You can not (yet?) mix formatting and/or links; meaning you can not set a text in ‘bold with a link’ or ‘bold and italic’
Please note the double return carriage between the lines
[this text has hyperlink](http://www.microsoft.com)
text not formatted
**this text is in bold** or __or another way to use bold__
other text not formatted
*this text is in italic* or _or the other way to use italic_
last text not formatted
++this text is underlined++