What methods can you use to check if a trading group or prop firm is reliable before signing up with them and giving them your money? Do they have to register with the SEC and FINRA (regardless of country)? Does that only apply to broker-dealers? I've gone primarily by reputation/market-presence. What would you do when considering a new or unknown firm?
The NFA offers a background check service on its members: http://www.nfa.futures.org/basicnet/welcome.aspx
Find out who's the oldest. I'd stand with someone who didn't get shut down, blow up their firm, or lose all their customers in the last 10 or 15 years.