Apple have not made it easy to create custom email signatures using their default email app on your desktop Mac computer.
In your Mail app > 'Mail' in the file menu > Preferences... Click on the 'Signatures' tab, add a new signature, give it a name and some holding text. In this example I have entered "replace me".
Quit your Mail app.
Now you will need to find this file which is on your computer.
My personal Mac is called PhilLeach so the folder path looks like this you will need to click through to locate the file.
Your file path will look like this:
***In your home folder (on my Mac the user folder is called 'PhilLeach'), you may need to change the folder view setting so that you can see the Library folder***
Hold down ctrl and click in the blank area of the folder > Show View Options > Show Library Folder
In your home folder hold down the command key and press J(cmd/⌘ + J) > Show View Options > Show Library Folder.
When in the 'Signatures' folder you will see a .mailsignature file. Make a copy of this file and paste it somewhere else such as your desktop.
Open the file in a plain text editor such as TextEdit on your Mac. I use a text editor called Atom. In the 1st screen shot of this lesson you can see where I entered the text "replace me".
Here is where you can enter your HTML to make a beautiful HTML email signature in between the <body> tags.
Save the file as the exact same file name.
Select the file, in the File menu > 'Get Info' or hold down the command key and press I (cmd/⌘ + I). You will need to choose to 'Lock' the file.
Overwrite the file in your Signatures folder.
Open your Apple Mail app and your email signature will now look beautiful (depending on your own HTML code!)
If you have an iPhone or iPad, send an email to yourself from your desktop Mac which has the email signature in the body of the email. Select all by holding down and selecting everything, then choose to Copy.
In Settings > Mail > Signature, Select the signature and tap in the form area so that you can choose to paste.
Hey presto! You now have a beautiful email signature rather than letting recipients know that the email was "Sent from my iPhone" default.