How do I add signatures

From Mail Help:

Create and use email signatures in Mail on Mac

You can create prepared text, called a signature, to include when you send email messages. For example, you can create one signature for your work email and another signature for your personal email.

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Create signatures

1. In the Mail app on your Mac, choose Mail > Preferences, then click Signatures.
2. In the left column, select the email account where you want to use the signature.
3. If All Signatures is selected when you create a signature, you’ll need to drag the new signature to an email account before you can use it.
4. Click the Add button below the middle column.
5. In the middle column, type a name for the signature.
6. The name appears in the Signature pop-up menu when you write a message.
7. In the right column (the preview), create your signature.
8. You can use the Edit or Format menus in Mail to change the font or layout, turn text into links or check spelling. To add an image, drag it into the preview area.

If you want your signature to appear after the original text of messages you reply to or forward, unselect the “Place signature above quoted text” tick box.

Delete signatures

1. In the Mail app on your Mac, choose Mail > Preferences, then click Signatures.
2. Select a signature in the middle column, then click the Remove button . 

When you delete a signature from All Signatures, it’s deleted from any account that uses it.

Automatically add a signature to emails

You can choose a signature to automatically add to messages you send.

1. In the Mail app on your Mac, choose Mail > Preferences, then click Signatures.
2. Select an account in the left column.
3. Click the Choose Signature pop-up menu, then choose a signature.
4. If you have more than one signature for an account, Mail can automatically alternate between them — choose At Random or In Sequential Order from the pop-up menu.

If you want to stop having a signature automatically added to your messages, click the Choose Signature pop-up menu, then choose None.

Note: A signature isn’t automatically added to messages you send from a unique, random address created with Hide My Email.

Add a signature to emails yourself

1. In the Mail app on your Mac, click the Signature pop-up menu in the message you’re writing.
2. Choose a signature.
3. If an expected signature isn’t shown in the pop-up menu, choose Edit Signatures to open the Signatures pane of Mail preferences, then verify that the signature is in the account.

Remove a signature from emails

1. In the Mail app on your Mac, in a message you’re writing, click the Signature pop-up menu.
2. Choose None.

Depending on how a recipient’s mail server handles signatures, your signature may appear as an attachment or image to the recipient.

If you use iCloud Drive on your Mac and other devices and have Mail selected in iCloud Drive options, your signatures are automatically updated and available on those devices. See Use iCloud Drive to store documents.

If you need to send a signed PDF document, you can use Markup in Mail to create a handwritten signature and add it to the document. You can also use the Preview app to fill out and sign PDF forms.

MHFapplehelp wrote:

How do I add signatures in Apple Mail

Create and use email signatures in Mail on Mac - Apple Support