Which of the following is an example of subscription in a letter?

The correct answer is Option (4) → Yours faithfully

The subscription (also called the complimentary close) is the polite phrase that ends a letter, written just above the signature: Yours faithfully or Yours sincerely in formal letters, Yours lovingly or Yours affectionately in personal ones.
Example: She ended the letter with the subscription "Yours sincerely" and signed it.

Why the Other Options are Incorrect?

Option 1: 12 A, Model Town — Incorrect. This is part of an address, which belongs to the heading of the letter.

Option 2: Dear Sir — Incorrect. This is the salutation, the greeting at the beginning.

Option 3: Requesting issue of duplicate Driver's Licence — Incorrect. This is the subject line of a formal letter, which states its purpose.