Unless stated otherwise, all information herein is taken from Crossroads of Twighlight, Glossary.
Da'covale, “'One who is owned'”, or perhaps “person who is property” in the Old Tongue, are Seanchan slaves. Many are hereditary, but anyone can become da'covale if they oppose the Empire in some way. For example, the Illuminators and two of Tuon's siblings had been made da'covale (WH, Ch. 14). Despite being technically property, it is possible for some such to have positions of great power. Some individuals, such as the human members of the Deathwatch Guard, some seekers, and so'jhin are in this group.
Da'covale who are property of the Imperial Family are specifically marked with raven tattoos (TSR, Ch. 38).
"To wear the ravens was to be the property of the Imperial family. There was an old story of a fool young lord and lady who had themselves tattooed while drunk, some three hundred years gone. When the then Empress learned of it, she had them brought to the Court of the Nine Moons and set to scrubbing floors. This fellow might be one of their descendants. The mark of the raven was forever." (The Shadow Rising, Chapter 38).