You can sign your tax return electronically by using a Self-Select PIN, which serves as your digital signature when using tax preparation software, or a Practitioner PIN when using an Electronic Return Originator (ERO).

Self-Select PIN - Use the Self-Select PIN method when you're using tax preparation software. The Self-Select PIN allows you to electronically sign your individual income tax return by selecting a five-digit personal identification number (PIN). The PIN can be any five numbers (except all zeros) that you choose to enter as your electronic signature PIN.

If you're filing a joint return, you and your spouse use your own PIN. As part of the authentication process, you each also enter your date of birth, identity protection personal identification number (IP PIN), if applicable, and either your:

• Original prior year adjusted gross income (AGI) or
• Prior year PIN

Practitioner PIN - The Practitioner PIN is a method that paid preparers use and doesn't require a prior AGI amount or prior year PIN. When using an ERO, you must always complete and sign an authorization form such as the Form 8879, IRS e-file Signature Authorization. Under this method, you authorize your tax practitioner to enter or generate your PIN. 

Refer to “Requirements for an electronic return signature” in Publication 17 for more details on signing your return electronically.