Make A Signature File on Mac [Step-by-step Guide]

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Looking to add a professional email sign-off, sign PDFs without printing, or generate a cryptographic .sig file to prove file integrity? 

macOS gives you several built-in ways to create "signatures," from simple text blocks to legally usable ink-style signatures and even command-line cryptographic signatures. This guide walks you through each method step-by-step.

How to Create a Signature File on Mac

Signatures on Mac:

On a Mac, "signature" can mean different things depending on context:

  • Email signature: A styled block of contact info automatically appended to messages.
  • Digital handwritten signature: Your scrawl is captured once and reusable in PDFs.
  • Plain .sig file: A simple text file containing your sign-off.
  • Cryptographic signature: A mathematically verifiable file signature proving authenticity.

How to create a signature file on Mac

Below are the best ways from iBoysoft to create a signature file on Mac.

Method 1: Create an Email signature with Mail

For the Email signature, you can:

  1. Finder > Applications > Mail app.
  2. Go to Mail > Settings > Signatures.
  3. Select an account in the left pane, then click +. 
    Create sig file with Mail
  4. Enter your signature (name, title, phone, links). You can format text and paste a logo.
  5. Drag the signature to the desired account if needed.
  6. In Choose Signature, set a default for New messages and Replies/Forwards.

Method 2: Create a digital signature with Preview

This is the most common need. You can use the built-in app Preview to realize this:

  1. Open any PDF (You can convert your file to PDF) in Preview.
  2. Click the Markup toolbar (Pen icon) > Sign (signature squiggle). 
    Create sig file with Preview
  3. Choose how to create your signature: 
    Trackpad: Draw with finger. 
    Camera: Sign on white paper and hold it up to your Mac's camera. 
    iPhone/iPad (Continuity): Sign with your finger or Apple Pencil.
  4. Click to insert the saved signature into the PDF; resize and position it.
  5. File > Save to keep the signature applied.

Learn more about how to do an electronic signature on Mac.

Method 3: Create a .sig file with TextEdit

This is the easiest way to create a file on Mac TextEdit:

  1. Finder > Applications > TextEdit.
  2. Format > Make Plain Text. 
    Create sig file with TextEdit
  3. Type your sign-off.
  4. File > Save...and name it signature.sig or signature.txt.
  5. Store it somewhere easy to reach (Documents, iCloud Drive).
  6. Paste from this file into apps that don't support built-in signatures.

Method 4: Create a sig file with Terminal

Use this in Terminal when you need a verifiable signature that proves a file's integrity and authorship (software releases, contracts, archives).

Below creates a detached signature file.sig for file.pdf using a private key.

  1. Finder > Applications > Utilities > Terminal.
  2. Type: 
    # Create a 4096-bit RSA private key 
    openssl genrsa -out private_key.pem 4096 
    # Derive the matching public key 
    openssl rsa -in private_key.pem -pubout -out public_key.pem
  3. Then create a detached signature for a file: 
    # Replace file.pdf with your target file 
    openssl dgst -sha256 -sign private_key.pem -out file.sig file.pdf
  4. Verify the signature (what a recipient would do): 
    openssl dgst -sha256 -verify public_key.pem -signature file.sig file.pdf

Moreover, you can scan your handwritten signature with Continuity Camera, Notes app on iPhone, or a Flatbed scanner, then export the image to your file with Preview.

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FAQs about creating a signature file on Mac

QWhat's the difference between a text .sig and a cryptographic .sig?
A

A text .sig is just a block of text you paste. A cryptographic .sig is a mathematical signature that verifies file integrity and signer identity with keys.

QIs a Preview signature legally binding?
A

Often yes, but laws vary by region and context. For formal/legal use, ensure the receiving party accepts it or use a dedicated e-signature platform.

QCan you create a signature in Mac Pages?
A

Pages itself doesn’t have a built-in signature tool. You can insert a signature in Mac Pages by creating one in Preview first, saving it as an image (PNG with transparent background), and then dragging or inserting it into your Pages document.