The string appears to be a metadata tag for a Japanese adult video (JAV). It can be broken down as follows: SONE-270 : This is the product code (ID) for the video.
The presence of "rm" and "jav" could imply a video or media reference, possibly from a specific platform or related to Japanese adult video content, given that "jav" is commonly used to denote Japanese AV (adult video). sone270rmjavhdtoday023141 min
Mara checked her phone. The station cameras archived footage for only 48 hours. She could still access it—she had friends who knew people. At the edge of night, the footage played: a young man, rain on his shoulders, pressing a hand to the clock’s glass, his breath fogging the face. Behind him, a little girl watched. He turned and mouthed something—"Sone"—then vanished into the crowd. For an instant he looked right at the camera, and his eyes were exactly Mara's age. The string appears to be a metadata tag
If you were looking for technical hardware instead, "Sone 270" is also associated with Broan Utility Fans Mara checked her phone
On the seventh stop—the playground with the rusted swing—she found a photograph taped to the underside of the seesaw. The picture was worn but intact: the young man from the footage kneeling, holding a baby. Written on the white border in a hand she could almost recognize was: "If you listen for 270 minutes, you'll hear what we couldn't say."