You can use PCB traces to create a poor mans spark gap on a PCB really easily. Whilst not as good as a proper device such as a gas discharge tube, they cost nothing as long as you have the PCB space available. Using a 8 thou / 0.2mm gap will create a spark gap that will arc at around 2kV. That's very approximate of course, but its certainly better than nothign and if the IC your signals are connecting to has good ESD protection built in it might be just the job at protecting it from higher voltage spikes its not happy with.
The spark gap wants to be very near the input, way before the signal get to the the electronics you are trying to protect. It doesn't have to be inline, you can happily come off the other side of a connector to place the spark gap, just kep it as close as possible.
Method 1 – Just place a fill next to a connectors pins and remove the solder resist
Its OK, not ideal but not terrible either. Ensure the solder resist is removed though as solder resist is an excellent insulator and you need the air gap for the spark to happen.
Method 2 – More arc points
Many designers prefer multiple points though, as after a prolonged arc a single point will carbonize. Arguably its not such an issue for discharging human static build up, but then again why not do it better if you can. Also bear in mind that human static charge can get up to 10kV or even 20kV, so whilst very brief there can be a lot of energy dissipated.
Alternatively create a linear gap with a constant gap so there is no single point to become carbonized and stop its effectiveness.
Letting the pads be soldered, whatever design you use, will help as it provides a higher area for the arc to come out of and creates more thermal mass which will reduce carbonisation by heating when an arc occurs.