Unfortunately, if they see the code to run the system, it doesn't really matter if they legally own the code or you legally own it. Once they have a copy, they can trade it even if you own it, because there is really no way you can prove otherwise.
If they run a server somewhere to trade it, there is no way you will be able to prove it in court. Your only real option is to trade it yourself and build a money management history, then become a trader with a bigger fund who likes what they see. Or, sell your trade signals through a service such as collective2.