For reference, informal votes were around 5% in our last federal election:

https://results.aec.gov.au/27966/website/HouseInformalByStat...

This article contains a fun breakdown of the types of informal votes including a category for "the usual anatomical drawings" (0.7% of informal votes):

https://www.crikey.com.au/2025/04/22/2025-federal-election-p...