"were marked as" is correct and usable in written English.
You can use it to describe an action that has already taken place. Example sentence: The trees with yellow leaves were marked as diseased.
Following the first round of the modified Delphi survey, 14 tests were marked as include and 28 tests were marked as exclude.
Consequently correct answers given by pupils were marked as incorrect as they did appear on the list of "right" answers.
Separate specimens with histologically confirmed normal tissue were marked as well.
Some were marked as being good for specific things, such as baking or roasting.
They alerted inspectors, who found the missiles in containers that were marked as fireworks.
"I grew up where there was a stigma attached to being the newcomer; you were marked as an outsider.
Samples were marked as sol-gel.
Thousands more were marked as "unknown," regarding their citizenship.
The catalysts obtained were marked as Pd-Cu(P /RGO.
Specimens were marked as either fractured or non-fractured.
Values exceeding these numbers were marked as outliers.
