Partial and unsatisfying answer. There's a firm connection between saliva conductivity and ovulation. It's well known and forms part of a natural family planning method called 'CUE'. This article seems to answer the question about conductivity changes after birth, but the full text is behind a paywall.
How about actual tattoos? Black ink would be conductive, I'd think. Lamp black. Other colors, maybe not. Does a broken bone heal faster in a tattooed arm?
How about masseurs? Have they found that using a high-carbon or high-conductivity oil works better? Nothing at all from the web. I remembered that I have a sample of 'aromatherapy oil' which may not be the same as massage oil, though it certainly smells wonderful.
Tried a quick semi-scientific experiment. Brushed a strip of this oil onto a piece of paper, (dark strip in center) then licked a similar strip on the right and used a sponge to put plain water on a similar strip to the left. Checking with ohmmeter (pointy probes, about an inch apart) showed about 6K resistance for saliva, 40K for the plain water, and no conductivity at all for the oil. I tried over and over, with probes nearly touching, pushing hard into the surface. Open circuit all the way. If this is the same sort of oil masseurs use, I think they're missing a bet. Saliva is 4 times more conductive than water. Nature does things for a reason.
If a masseur is reading this, try infusing some graphite powder or wood ash (close to pure carbon) into your oil and see what happens.
The current icon shows Polistra using a Personal Equation Machine.