I don't think it would be a decision of a local body of elders as the trolleys came from various congregations.
Depending on where the carts are, they are either governed by a single congregation, or by the central committee for public witnessing that governs the city centre and touristic hotspots.
The JW that watch the cart in my city come from quite a few congregations, including from out of town. Their efforts, permits, locations, etc. are coordinated by a central command for the whole city.
If central command for the city says 'put this ugly label on your carts' then they will have the ugly label.