HTML Email Signatures can't be added to some mobile devices. If you'd like a text-only version of your signature created for mobiles, let your Project Manager know.
As mail clients don't take signature settings from Webmail, if you use a mail client like Outlook or Apple Mail, you'll need to add the HTML to the program settings yourself. For support on the 3rd party mail clients, you will need to contact the service provider. Toolkit Websites only support Toolkit Webmail and Mozilla Thunderbird.
Finally, how your email signature shows for different recipients will depend on their device/mail client settings. Some may instruct their mail client to block all images, rendering your email incomplete until the recipient approves the images. Others may instruct their software to automatically render the complete email signature. Neither you nor we can control how your recipients mail programs show signatures.