^Well, no, they can't as the Guardian article makes clear - TFL requitre them from any company doing work for it, so they end up on small vans where 'stay back' makes little or no sense. Companies could choose to do no work for TFL, I suppose.
Anyway, they are not warning stickers, they are worded, at best, as advice and at worst as an order. They don't warn about anything.
^Well, no, they can't as the Guardian article makes clear - TFL requitre them from any company doing work for it, so they end up on small vans where 'stay back' makes little or no sense. Companies could choose to do no work for TFL, I suppose.
Anyway, they are not warning stickers, they are worded, at best, as advice and at worst as an order. They don't warn about anything.