Ability to add href sms link to signature

I wanted to be able to create clickable links in my signature. Was able to create a telephone link <a href="tel:+1xxxxxxxxxx" rel="noopener noreferrer">Call</a>, but not a link for sms <a href="sms:+1xxxxxxxxxx" rel="noopener noreferrer">Text</a>. Deletes the code when saved.