Okay, maybe spreading our message helps too but really what we need to do is get everyone else to see and hear what is going on. I'm exposed to it in real life in the LGBT "community", some other groups (e.g. women prisoners) are feeling the brunt of it and we see the craziness online but a lot of people will be oblivious until the point where it directly affects them and then it could be too late.
When the message 'transwomen are women' was projected in London, women were talking about having a gender critical/pro-women counter message but I think what would have worked better would be to project some of the transactivists' own beliefs up there to get people thinking (e.g. "the penis is a female organ").
At Pride what we need (and what Stonewall would do if they thought the public would actually buy their message if they knew what it really was) is t-shirts saying "Some women have penises.....get over it". Or "real lesbians like ladydick". Those in charge can't dispute those messages because they believe in them (and they'd get too much abuse if they tried). However, I think at least the leaders realise that they can't go around promoting those messages at Pride because the audience of straight people and older, married gay/lesbian couples whose only contact with the "community" is coming to Pride once a year will think "hang on, what's going?"
Where companies have replaced 'single sex' with 'single gender' I think women who expect single sex, say, sleeper carriages or hostel dorms should be warned of this - but, if the companies are so proud of their stance, they should want to shout it from the roof tops.
Instead of posting gender critical posters/stickers that will be taken down, why not stick up notices on their behalf explaining their policy.
E.g. in the women's dorm "Hostelling Scotland promotes an inclusive environment which welcomes anyone who chooses to be recognised as a women [their words btw!] into the women's dorm and showers. We recognise that some women have penises and welcome women with penises into these facilities."
What argument would they have for taking that poster down? It merely states their policy without offering a counter-argument - because it doesn't really need one.
Even on social media, if you aren't brave enough to be openly gender critical, you could share some of the crazier transactivist articles - either voicing your support for them (if you don't mind some of your friends thinking you are an idiot) or just saying something vague like 'interesting article', 'this is a new perspective' etc.