We have something similar in Barcelona (maybe entire Spain? Apparently called NaviLens, colored squares rather than triangles) all around public transit points. They're used for blind people to navigate the public transit system :)

> As users sweep their environment with a smartphone, audio cues allow them to find and center the tag in the phone’s field of view. A shake of the wrist prompts the details contained within the tag to be read out (visually impaired people are often holding a guide dog or cane with their other hand). https://www.technologyreview.com/2019/06/06/135057/these-col...