If it is an "across the line" device, what does the 20 mA specify?
I believe it is a non-linear resistance element of some kind, but I don't think it is likely some kind of surge supressor.
If you accept that I might be a million miles out and totally wrong.
When I read through a bunch of the datasheets, by that brand, the 20mA's, seems to be what we would call (in English), the maximum continuous current, for the device.
Which follows through logically, because the datasheet was (for the device I was looking at), around 2.9 Watts max dissipation, at around 100 volts, hence 20 mA's doesn't sound too unreasonable.
Although this might be an unexpected parameter, don't forget these are probably components from a rather long time ago, different manufacturer so does their datasheets differently.
Also there are even graphs, showing the current (in mA's vs highish voltages).
I'm not clear if these currents (20 mA's) are suppose to flow, because these are old non-linear resistor devices, rather than modern MOVs, or if it is unwanted leakage currents, increasing at higher voltages, because they are very old devices.
Or I'm completely wrong. (Because the datasheets are rather brief and seem to be Japanese originally, I'm having partial difficulty understanding them).