Here is the workaround to create HTML signatures for Outlook 2007. When you create a signature in Outlook 2007 it creates 3 separate files (.htm, .txt and .rtf). To create a more custom signature you can write it in HTML – this is especially useful for when dealing with graphics and advanced formatting.
How to create signature in Outlook 2007:
- In Outlook go to Tools > Options and the Mail Format tab.
- Click the Signatures button.
- Click the New button.
- Give your signature a name like ‘MySignature′
- Click on OK
Outlook doesn’t require any content to be added and will create the 3 individual files. Click OK and close Outlook
How to Locate your signature folder: Copy one of the following lines depending on what your operating system is.
- Windows 7: %userprofile%\AppData\Roaming\Microsoft\Signatures
- Vista: %userprofile%\AppData\Roaming\Microsoft\Signatures
- XP-2003: %userprofile%\Application Data\Microsoft\Signatures
Click on Start and then Run – paste the line you copied into the Run box and hit Enter
You should see 3 files created for your "MySignature” file (in .htm, .txt and .rtf formats). If you can’t see the file extensions, go to Tools / Folder Options / View and untick ‘Hide extensions for known file types’, or right-click the file and select ‘Properties’ to determine the file type.
Replace the HTML file created by Outlook:
Take your HTML signature file and use it to replace the .htm file in your signature folder (i.e. save it as in this system folder, using the same filename as the .htm signature file created by Outlook ).
To start using your new signature:
Restart Outlook.
It worked for me on Outlook 2007 and Outlook 2010. Hope this is useful for you 
