Signals are edge objects that can be attached to tracks.
For the visual representation, they have a special set of event data for animations too.

signal animations
Especially for signals the animation events are an important aspect. They can be used in mesh nodes to support the visualisation of the two signalisation states 'red' and 'green':
forever animation is used for any permanently looped animation.idle_red animation is used as a loop while the signal is in 'red' state.green animation is used when the signal switches from 'red' to 'green'.idle_green animation is used as a loop while the signal is in 'green' state.red animation is used when the signal switches from 'green' to 'red'.
While the forever animation runs constantly, the other four events form a loop. Usually a signal is in red state and the idle_red animation is performed. As soon as it switches to green, green is performed once. Then idle_green is looped as long as the signal stays green. When the signal turns back to red, red is performed once before idle_red is looped again.
The idle animations can be used e.g. for blinking signals.