E-bike problems and the police, is going to be like peeling an onion. The more layers you go through, the more difficult the situation, and the more difficult your withdrawal.
First layer, don't be conspicuous...... Don't get noticed....
Don't overtake a police vehicle that is doing 30mph on a road with a speed limit of 30mph. Don't ride a bike during daylight hours with a hub motor large enough to pull an articulated lorry.
Don't ride recklessly. This is an offence with or without a motor.
If you get noticed, what will get you stopped or spoken to? Having an accident, with or without someone else involved. Riding recklessly in front of a police officer.
Once you have been approached, there is either going to be some general interest which may or may not be personal interest ("I've been thinking about buying one of these"), or you will be losing another layer of the onion as the officer has previously noticed you flying around town and has decided you might be breaking a law or two....
I surmise, any pedelec (a purpose built bike/trike, within EN spec) already has all the labelling it needs. Those fitted with aftermarket kits are the ones that need labelling. Mid-drives must have some flat space where additional labelling can be fixed surely, if required? Duplicate labelling can be fixed to the hard cases of battery packs if there is a hard case to label. Clear silicone should provide enough adhesion to keep the labels in place without damaging the plastic. Hub motors if they don't already have labelling, the flimsy silver labels that can easily be stuck to the hub are suitable enough?
Unless there is a specification that says otherwise, surely this labelling is a bit like learner car drivers or learner motorcycle riders having to display "L" plates. As long as they are clearly visible, there's no hard rule on where they are placed?
Like motor vehicle drivers caught with no insurance, if you have been caught riding an e-bike at 35mph without using your pedals and weren't on a steep downhill slope, you likely are not going home with your e-bike whatever the "label" says?
I think law-abiding riders have nothing to worry about, just like law-abiding car drivers. The police are not looking for a problem, unless one lands at their feet. Crash, or ride so dangerously someone chooses to ring the police to alert them to you riding style, will get you unwanted attention. Best avoid both situations?