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.