Likely just double sided tape. That would gather dust where exposed, (not stuck to wires, bit) though. As I found out from doing the same thing with a super long lamp cable, in my bathroom, where we only had a heatlamp, and that sucked in summer. But also the power point was in an awkward place, so I dangled a lamp from the ceiling, but after taking it down, and being too lazy to remove the tape, now it's fly catching tape.