The "traffic signal" was spotted by a British UFO enthusiast named Joseph White.
Curiosity, while busy scanning the surface, snapped the photo.
"I have been following the images from NASA since the start and I flick through them on the NASA website every day," White told the Western Daily Press.
"I saw this one and I thought 'Hang on, that looks a bit strange," he added.
As we wait for NASA reply, in all probability, it looks like another rock, the report added.