It means no state tax was withheld. Whether it is taxable by your resident state or not depends on your State of Legal Residence.
From a tax standpoint, your State of Legal Residency (SLR) is considered your "domicile" or "resident" state as long as you are on active duty. Even if you are stationed in another state, you’re still considered a resident of your SLR (Home of Record).
To find out if you need to file a state tax return when you aren't stationed in your resident state, check out Military Filing Information on State Websites, which has links for active duty military and their spouses in each state. If you have nonmilitary earnings, review Civilian pay earned by active duty military.