Following these steps should allow you to insert a graphical logo in your signature when working via web browser to your Office365 e-mail account. Adding a graphical signature is often desired to present a professional image.

Steps to Add Logo To Signature

1. Upload the logo to a public access url. You can post this to the images directory of your web site and then linke to it. Your url then would behttp://www.myDomain.com/images/logo.jpg
2. In Outlook 2010, compose a new email and mark sure the Format Text is HTML. ClickInsert>Picture, paste the URL of the logo in the File name tab and click Insert. Please send the email to the Office 365 email address.
3.  In Outlook Web App, double click the email, right click the logo and click Copy. ClickOptions>See All Options>Settings. In the E-Mail Signature edit box, press Ctrl+V to paste the logo. Mark the Automatically include my signature on messages I sendoption. Make sure HTML is select behind Compose message in this format. Click Save.
4. Send an email to check the result.