To fix this issue, you will need to remove and reformat the graphics in the Outlook signature.
Remove and Reformat the Outlook Signature
Open Microsoft Office.
Click File, Options, Mail, Signatures.
Click the signature you want to edit, then make your changes in the Edit signature box. You may need to remove the graphics or redo the graphics using a different file format.
When you're done, select Save, OK.
If this does not fix the issue, run a repair on Outlook.