unmarked

My mother died when I could not have been more than eight or nine years old, on one of old master's farms in Tuckahoe, in the neighborhood of Hillsborough. Her grave is, as the grave of the dead at sea, unmarked, and without stone or stake.

1855, Frederick Douglass, chapter 3, in My Bondage and My Freedom. […], New York; Auburn, N.Y.: Miller, Orton & Mulligan […], →OCLC

The “little green men”—faces covered, wearing unmarked olive uniforms, speaking Russian and using Russian weapons—have played a significant role in both the occupation of Crimea and the civil war in eastern Ukraine.¹⁹⁶

2015, Shane R. Reeves, David Wallace, “The Combatant Status of the “Little Green Men” and Other Participants in the Ukraine Conflict”, in International Law Studies, US Naval War College, volume 91, number 361, Stockton Center for the Study of International Law, archived from the original on 27 May 2022, page 393

For instance, from the semantic point of view the words dog and bitch are unmarked and marked for the contrast of sex. The word dog is semantically unmarked (or neutral), since it can be applied to either males or females (That's a lovely dog you've got there: is it a he or a she?).

1968, John Lyons, Introduction to Theoretical Linguistics, Cambridge University Press, →ISBN, page 79