Sorry to be the bearer of bad news, but it doesn't actually matter, Captain.
There are thousands of signal-providers "out there" (and unfortunately quite a few "in here" as well!), and given the huge number of them, there will obviously always be some who have a decent, profitable history for (say) 6 months, just by chance, but the point is that there's actually no logical or statistical reason to imagine that they'll also be the ones any more likely to be profitable over the next 6 months. Which is, of course, what actually matters if you're thinking of subscribing to one.
It's just random.
People like to imagine that "surely" one with a good history is more likely to have a better future, but it isn't actually so at all.
That's just like imagining that a "managed fund" with a good history of trading on the stock exchange one year is more likely than average to make profits in the next year, but there's an overwhelming panoply of evidence to prove that that just isn't so: they're no more or less likely than average, overall, to be profitable going forward.
Key concept: if someone actually had a genuinely profitable "signal service", they'd be raising capital to trade it successfully themselves (which is very easily done, these days, through businesses like TST and their competitors) rather than selling it to subscribers for $29.99 per month, or whatever.
It's a lovely dream, to imagine that one can somehow identify a profitable signal service and then steadily make money over the long term, just by subscribing to it, with nothing else to do but duplicate the trades, but it doesn't happen on this planet and there are reasons for that.