Function place_signal 

pub fn place_signal(
    cmd: Commands<'_, '_>,
    pos_indicator: Single<'_, '_, &TrackPos, With<PositionIndicator>>,
    q_segments: Query<'_, '_, &mut SignalsManager>,
    target_segment: Res<'_, TargetSegment>,
    assets_manager: Res<'_, AssetsManager>,
    next_editor_state: ResMut<'_, NextState<EditorState>>,
)

Places the signal on left click.