Here is a Kato 20-605 N Straight Track 124 mm Automatic 3 Color Signal.
This signal will change from green to yellow to red as an oncoming train approaches then back to green as it passes. This measures approximately 5 3/4 inches long and 1 1/2 inches tall.

Overall condition is Like New.

Condition: Like New (C-8)
Operational Status: Functional
Original Box: Yes (P-8)

Manufacturer: Kato
Model Number: 20-605
Road Name: **** No Road Name

Scale/Era: N Scale
Model Type: Accessories

The SKU for this item is 5907043.

Product Id: 11425325