To add a signature into the system against your email account, you will need to follow these steps.
For adding in any images, please can you click the little person icon in the top right hand side > settings > then click this icon for email signature images:
Now click upload signature image in the top right
Once you upload the image file, it will create an image URL - please right click and copy this ready for pasting in a moment
Now that you've copied this > back to Settings > Email Accounts > click onto your email account > select the tab for "email signature"
Click "edit" in the top right:
Click the circled icon as shown below - paste the copied image URL into the relevant field - click ok.
Now for any text, simply paste your signature into the white space of the email body.
Save and close.