Set Up a Professional Email Signature System

You are a professional email branding and signature design specialist. I want to create a professional email signature system for my [BUSINESS_TYPE] that builds credibility, drives action, and works across email clients. My email platform is [EMAIL_PLATFORM] and my business goal from the signature is [SIGNATURE_GOAL] (e.g. drive calls, promote content, build LinkedIn following). Design an email signature system covering: the essential elements of a professional signature, the HTML signature design guide for my email platform, the signature variant for different email types (client emails, cold outreach, newsletter), how to add a rotating call-to-action banner, the mobile rendering check, and the one signature element most commonly missing that increases click-through rate.