The clever little marks are carved all over Skyrim. mostly on the doorframes or fronts of buildings, but you can find them pretty much anywhere a thief's been. It's the way we talk to each other without talking. Keeps the newer thieves from becoming dead thieves and all that nonsense.. This mark indicates a safe house, entrance, or contact with the Thieves' Guild and indicates that the area is friendly to or serves as property for the Guild. One of the most notable examples is the sarcophagus sign that acts as the secret back entrance to the Ragged Flagon's Cistern. It can also be seen on the doorway to Riftweald Manor, which is owned by the sometime Guildmaster, Mercer Frey.
This is because, upon completing the Silver Linings quest in Skyrim, Endon is the local guild fence for Markarth, and is therefore provided sanctuary by the Thieves Guild. Though often overlooked, a knowledge of Shadowmarks can make The Elder Scrolls V: Skyrim a more immersive and interesting experience for any would-be rogue.. Shadowmarks are a series of symbols that the Thieves Guild inscribes for a variety of reasons—usually around doors or specific buildings. They act as a series of codes that previous thieves have left to assist future thieves, such as warning of danger or pointing out houses with valuables inside. The legend for the code is outlined in a book of the same name, authored by Delvin Mallory.