Rather than a PO Box you could try one of the various 'Virtual Office' services in the London area, so you get a mailing address and telephone answering, eg http://www.voffice.com/
Im not sure why you even need an address in London. Your services will be delivered over the internet and you will most likely use paypal or credit card as payment methods so no one is really going to care where you're located. Paypal provides added insurance for online purchases also. I'd just say something like 'We're a global company with expert traders providing expert market commentary across all major international currencies.'
I woudl want a London address to increase my credibility...certainly not the Russian addresses) but if I can get away without showing any kind of the address, that will be fine with me as well!) I do not plan to stay at any place for long if all goes well...
and here is what the major USA fx signal had to say about being regulated by NFA (and they are at the top of the search in Goggle for fx signals): In answer to your question; we are located in the USA. Since we are a Forex signal service provider and not a boker, we are not required to be under the NFA regulation. That is how the major USA forex signal provider replies about being regulated....and they have the clients all over the world....I think I will surely proceed to creating a EDUCATIONAL SERVICE WITH PRECISE ENTRY SETUPS that will teach the traders to trade them on their own...
maybe someone here has A SIMILAR experience setting such kind of service? It woudl be wonderful to talk!)