I can't see anything on RTBU socials or website, but updates on there have seemed spotty/delayed when I've checked in the past, so that's not definitive. They're still bargaining, so it's possible.
They have a page for current industrial action on their bargaining campaign website: https://fightingforourfuture.com.au/current-industrial-action/
Right now, this is all it lists:
The below actions came into effect on 0001hrs on 11 September:
- Wearing union gear to work – indefinitely
- Placing stickers or other union/campaign material on Railway assets (so long as it does not affect safety) – indefinitely
- Speaking to members of the public or the media about campaign or union matters – indefinitely
So the union shirt is just an ongoing thing and doesn't necessarily indicate something's happening today. Next time, if you've got time, just ask the union member what's going on (as per point 3).
EDIT: I should say also that they posted a bargaining update for yesterday, and it doesn't say anything about further action either. See here: https://fightingforourfuture.com.au/member-updates/nsw-and-sydney-trains-bargaining-update/