You can't find them anywhere else in the city and people are curious.
"I haven't seen anything like that and I come through here every day," said Shawn McLaughlin of Boise. "I honestly don't know what they are."
We didn't know either so we asked the Ada County Highway District if this is the new normal for traffic light looks.
It turns out a lot of drivers are running the red lights at 15th and Main, so the highway district is trying something new.
In the parlance of traffic engineering, they're called retro reflective back plates.
Their goal is to draw attention to the traffic signal and warn of a possible red light coming which is supposed to make people slow down and stop.
"This intersection is one that had a fairly high crash rate," said Christine Myron, spokeswoman for the Highway District. "It was No. 8 over the past five years in seeing the highest crash rate in Ada County. Among those crashes, people were running red lights, whether they didn't see the light or ran it intentionally, that was leading to crashes."
The highway district says studies around the country show the retro reflective back plates can reduce crashes by as much as 15 percent.
If their purpose is to be noticed, they seem to be working so far.