1. Open 'Thunderbird'.

2. Save the attached signature file that you received from SigBee website, in a folder your can remember.
(a known folder you will not mistakenly delete in the future)

3. Choose 'Account Settings' from the 'Tools' menu.

4. Check the 'Attach this signature' checkbox.

5. Click 'Choose'.

8. Find and open the signature file that you saved in step 2.

9. To complete the process, click 'OK'.