When I got caught a few years ago it was by a police motorcyclist. He was all in black with his bike parked behind him facing away from oncoming traffic so no hi-vis could be seen.
AFAIA Community Speedwatch rules can vary between forces but there are some common themes, some forces seem to add some more criteria:-
1. Volunteers must follow laid down rules of conduct. The safety of the volunteers and all road users is paramount, volunteers must not stand in the road at any time.
2. Approved high-visibility jackets must be worn at all times.
3. Volunteers will only use approved equipment and will only use the equipment following final approval by the Police.
4. Monitoring will only take place at locations approved by the Police.
5. Volunteers must not attempt to conceal their speed monitoring activities from passing motorists.
6. Monitoring is to be undertaken by a minimum of three volunteers at any one time.
7. It is strongly recommended that at least one volunteer be in possession of a mobile phone.
8. Monitoring only should take place. NO signals or gestures are to be made to drivers. Volunteers MUST NOT attempt to stop any vehicle.
9. Checks should be carried out in daylight hours and in 20mph, 30mph and 40mph speed limit areas only.