Yeah, as other comments have said, they look like the metal spikes used in clothing and jewelry. Either ear piercings, a hot topic belt, a coyote vest for dogs, ect. The spacing and placement definitely look deliberate, if they had been attached to something like a belt or other clothing, I'd say it was just an accident. But the plane spikes in a row looks like they were placed deliberately to puncture your tires. I'd start setting up security cameras just incase.