Polarity of gas discharge tubes

Photo attribution:
By Ceinturion 17:47, 19 August 2007 (UTC) - Own work, CC BY-SA 3.0, https://commons.wikimedia.org/w/index.php?curid=2587926
Small dot indicates "gas-filled". Likely at sub-atmosphere pressure. Its position within the schematic symbol doesn't suggest polarity.
These devices may include thoriated electrodes to reduce striking voltage.
So for this example: it is bipolar....strikes with either polarity.

Surge arrestor bulbs for lightning protection are symetrical usually. There are ones with three electrodes but in those, the third electrode is a shared ground, not an ignition electrode as in your examples. The schematic symbol is different then. See e.g. the this TDK/Epcos datasheet (last page).

In contrary, gas bulbs used for lighting purposes are sometimes symetrical, sometimes unsymetrical. See e.g. this Osram datasheet. Such bulbs may have an additional ignition electrode, which is the third electrode in your example.