https://www.irs.gov/newsroom/questions-answers-on-combat-zone-tax-provision

Civilian taxpayers covered by the relief provisions described here should put the words "COMBAT ZONE" and their deployment date in red at the top of their tax returns. Members of the military do not need to write "COMBAT ZONE" and their deployment date on the tops of their tax returns because the U.S. Department of Defense informs the IRS about members in the combat zone.