Instructions provided on the front of the SSN card stub advise adults to sign their card in ink immediately. Children are told not to sign until age 18 or their first job, whichever is earlier.
Although the card serves as SSA's official verification of the SSN assigned to the
individual named on the card, it is not an identity document. Failure to sign the
card does not invalidate it. Therefore, a card sent to an infant or young child may
be left unsigned and kept in a safe place with other important documents until needed
by the number holder for employment purposes.