Scope for a counter-campaign
My only experience of the Tube was on a holiday a long time ago..( at the very time they brought in the no drink bottles on airplanes, Getting through Heathrow as they tried to implement the new security theatre was traumatic, so timestamped quite thoroughly), and I recall noticing nobody speaking on the tube was using english - or at least any version intelligible to me.
Simply combine the tube-chat badge/logo with the red circled diagonal slash negation symbol (Ghostbusters-like), Variants could include the raised middle digit or a stamped FOAD in the style of MASH. Other designs will emerge as entrepreneurs get hold of the idea.
Make these available printed on buttons, Tshirts, backpacks whatever. Dodgy street vendors can selll them from the station entrances, adding to the local ambience.