Open this generator in Safari, fill your details, then choose Prepare for Mail. The next page selects the signature for copying, with the logo beside the contact details. Campaign tools can use Copy HTML source.
Wait for “Signature selected”, then Cmd+C. In Mail → Settings → Signatures, uncheck “Always match my default message font”. Click inside the signature field, Cmd+A → Delete → Cmd+V. Open a new compose window to check the result.