Its a little hard to work from your pictures (extreme angles, rather than flat)
But from that 4 pin connector at the bottom, you have Ground to plane, the fat trace will be power, The third pin connects directly to the pic microcontroller from what I can see, and while I cant see what the 4th pin does, I suspect another data line or as simple as not being present
If its 1 data line, I would expect something similar to K-line, an older industrial 1 wire protocol, Its pull down only,
If 2 wires, then maybe something else. if its direct to the CPU there are not many things it could be.