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Room markers are objects in The Sims 3 that look like shiny silver spheres. They dictate the behaviour of certain spaces on lots, and some have menus accessible via the ctrl + shift + c interaction.
Room markers can be added to a lot using the buydebug cheat.
Fog emitter[]
Tomb fogger[]
The tomb fogger was introduced in The Sims 3: World Adventures. Placing this object in a room will turn that room into a tomb room that is not visible until a Sim enters. A sound effect plays when Sims first enter rooms with this marker. Using the ctrl + shift + click interaction on this object allows builders to set different genres of tomb, such as 'Tomb of Death'. Changing this setting changes the message players receive when they first enter the room.
Puddle/Burnt Tile Marker[]
Introduced in The Sims 3: World Adventures. Can be set with Ctrl-Shift-click to either cause a small puddle underneath it, or to produce a purely cosmetic scorched effect on the floor tiles underneath it. Has no effect if placed above carpets, including the Into the Future quarter-transparent glass carpets.
Hidden room marker[]
This marker was introduced in The Sims 3: Late Night, and later backpatched into the base game. Placing this object in a room on a residential lot will turn the lot into an apartment and hide the room that it is placed in. If there is a door into this room it will act like townies live there.
Public room marker[]
This marker was introduced in The Sims 3: Late Night, and later backpatched into the base game. Placing this object in a room will turn a residential lot into an apartment and prevent players from editing the room in build or buy modes without using cheats. Also, any objects in the room will not count towards the lot value.
For unclear reasons, there's also an Island Paradise-specific clone of the marker object that works seemingly exactly the same.
Skip level room marker[]
This marker was introduced in The Sims 3: Late Night, and later backpatched into the base game. Placing this object in a room will turn the lot into an apartment and prevent the player from seeing the contents of this level.
Seasonal lot marker[]
Introduced in The Sims 3: Seasons, and later seemingly backpatched into the base game despite it being less than useless without Seasons. Automatically placed on lots when they are given the festival lot assignment (and does not go away when the assignment is changed to something else afterwards), and can be added to any lot assignment with Buydebug.
The presence of this marker will make editing the lot a whole lot more complicated, and borderline impossible without Buydebug, as Buydebug is needed for the marker to be visible, clicked on, and to enter Common mode.
For Buy Mode objects (but not most Build Mode objects), the markers recognize 6 states of existence: Common, Spring, Summer, Fall, Winter, and Construction (Construction does not usually appear to be in use on custom lots), all of which can have separate Buy Mode objects placed around that rotate seasonally. If in doubt about how to handle the situation, stick to Common.
Uncharted island marker[]
Introduced in The Sims 3: Island Paradise. In the Isla Paradiso archipelago, it is used to determine which islands that are unvisitable and covered by clouds until certain quests are completed. It is available in all worlds in not only Buydebug, but also in Edit Town mode, though it is not well studied how the marker would work like in non-Isla Paradiso, Maxis-created worlds.
Event Lot Marker[]
Available in the base game as of Patch 67, likely considerably earlier too. With a full name of "EventLotMarker DO NOT TRANSLATE", it was likely deprecated during the games' development.
Performance Jig Marker[]
Available in the base game as of Patch 67, likely considerably earlier too. With a full name of "performer_jig DO NOT TRANSLATE", it was likely deprecated during the games' development, replaced by functions built into show stages.[TS3:ST]