Six years ago, Providence restaurant The Hot Club started the custom of flashing its lights each night at 8:30, as a way to say good night to the children in the six-story Hasbro Children’s Hospital across the Providence River. The club would flash its neon sign, and patrons would gather on the waterfront deck to wave flashlights and cell phones.

Now hotels, boat traffic, skyscrapers, and police cruisers have begun to join in, some with permanent signals but many using handheld lights. About two dozen children are in the hospital on any given night, and they’ve taken to flashing back with lights of their own.

“No one knows who’s on the other side of the gesture,” hospital cartoonist Steve Brosnihan told the Associated Press. “People often say, ‘I get goosebumps hearing about this.'”

“They don’t know me; they could skip the step of flicking the lights, but they do it anyway,” said 13-year-old lupus patient Olivia Stephenson. “I hope they saw the thank you.”