It's easy to add HTML code into the signature designer. You can paste this code into both pre-existing signature configurations, and into new signature configurations.
NOTE: You can only edit the HTML of a block, so you must either create a new block or have a pre-existing block before carrying out the following steps.
1. Select your chosen signature and click EDIT or create a new signature by clicking CREATE NEW.

2. Click on the HTML code button - </>.

3. Paste your HTML code into the HTML Editor.
NOTE: To use fields from Active Directory, replace static user details in the HTML code with fields e.g. (!FirstName!).

4. Click on SAVE once you've finished editing the signature in HTML.

For an example of how pasting HTML works, feel free to follow the steps above with the contents of the .txt file below.

(See attached file: Example signature layouts.txt)
Related Products: CMS O365, Signature Designer v6.0