At my work just all me and my fellow techs in a meeting we basically expressed shared frustration at wages not increasing at all in last couple years despite the company making billions.
It appears we were all individually expressing this and it boiled over cause nothing was being done.
So are there any organizations collecting signatures or potential members with the goal of forming one later?
Advertising? Imagine if the source code for every open source project included an ad for unions.
Management probably doesn't look at the source code, so it's a good place to hide messages for fellow workers
Easy way to be identified, I wouldn't recommend that at this early a stage, especially in company code.
OP I suggest looking at other existing unions near your discipline and other countries that have unions for tech workers. If you look at how they have operated and achieved success, it may help you to navigate that in your world.
These are all long-fought battles with lots of lessons already learnt, find the people who have already fought them and you have a good starting point.