Outlook 365 (online)
1. Open the archive
2. Select the picture with the mouse until it becomes blue
3. Press CTRL+C
4. Go to https://outlook.office.com/owa/
5. Click on option, under the setting icon on the top right of the screen
6. Click on Email signature (under mail, layout)
7. Go at the end of the signature and press CRL+V
8. Save

Here's a similar video that show the step http://www.onbrandgroup.co.uk/files/video/guide365.webm


Outlook 2016
1. Open Outlook 2016
2. Compose a new email
3. Select the "INSERT TAB"
4. Click on Signature, signature
5. Open your signature
6. Select all the content
7. Copy it (CTRL+C)
8. Create a new signature and assing it a name
9. Paste your signature (CTRL+V)
10. Open the archive
11. Select the picture with the mouse until it becomes blue
12. Press CTRL+C
13. Go back to the signature you just created and named in Outlook
14. Go at the end of the signature and press CRL+V
15. Save