I dont like the negative signs on many london vehicles telling me not to undertake, frankly there are times when its actually perfectly safe to undertake (stationary) and the negative wording is like saying -dont press the red button- it just makes many humans want to press the button to see what happens OR to undertake.
Please find a polite encouraging sign, the awesome cyclist one is good, it makes it feel like the driver likes the fact you are part of the solution, not part of the problem and wants you there. This is nice. Ooooh lets be nice.
‘Awesome Cyclists’
Undertake me only if its safe.
We want you alive as it means less cars.
Keep riding.
I’m sure some marketeer can word it better! 😉