Gmail

1. Click the gear → See all settings
2. Scroll to Signature → Create new
3. Paste, then click Save Changes

Outlook Desktop

1. File → Options → Mail → Signatures
2. Click New and name it
3. Paste into the edit box → OK

Outlook Web

1. Gear icon → View all Outlook settings
2. Mail → Compose and reply
3. Paste into signature field → Save

Apple Mail

1. Mail → Settings → Signatures
2. Select account, click +
3. Paste into the right-hand panel