The forex market is particular popular with Copy Traders. The volume traded in those markets makes it highly unlikely any trader’s actions will distort the market. Currencies are an unregulated instrument so a trader that develops a successful strategy should be able to offer forex copy trading to a wider audience. The forex markets of course trade 24/5 (at least) and it’s easy to get started; developing a program to run a robo-trading strategy can be done with the aid of tools to support strategy modeling. ZuluTrade for example has a script/modelling function called ZuluScript that is a good place to start looking at automated trading techniques.
A trader that should happen to be successful in forex and attracts copiers, and then becomes a bigger player in the market will still struggle to distort the forex market. It’s good for ambitious traders to think big and ensure their chosen market has capacity to accommodate their very successful strategy. This is no guarantee of success of course, but it does at least show forward planning.
It is possible to trade other markets, for example at eToro it’s possible to copy trade in the following markets: commodities, indices, stocks, ETFs, crypto and of course, forex. As a side note, and just to demonstrate how much variety is available, AVATrade allow Automated, Semi-automated and Manual copy trading.
Certain trading styles suit certain markets. A successful trader, with an attractive risk-return ratio, long track record and transparent reporting is worth considering regardless of the market they operate in.
Approaching your question from a geographical perspective you’ll find Signal Providers operating in all markets. Again, there is a bias toward the more liquid markets but the traders looking to attract followers will be trading to make consistent returns in line with their strategy aims. Where that happens to be is of secondary importance.