The Plot Indicators show whether a Plot is powered, unpowered, or was powered and now unpowered. They are always at the bottom right-hand side of the plot, so looking at the Town Map you can see where they are.
The Plot Indicators show whether a Plot is powered, unpowered, or was powered and now unpowered. If a redstone block is shown under the lamp, that means the plot is powered. If no block is present under the lamp, the plot has never been powered. If a plot was powered and is no longer powered, a coal block will be present under the lamp.
If a plot is covered with a zone (i.e. Residential, Commercial, or Industrial) and the power plant powering that plot is destroyed or taken down, the plot will lose power, a coal block will appear under the lamp and the plot will become abandoned in a matter of seconds.