99% of "trading signals" are used by traders(or con artists) to pump or dump a specific coin/token for them to increase the likeliness of them winning their long/short position.
That is just what it is. The moderators and admins of such channels can buy some shit coins at a very cheap and ridiculous price in large unit and they will call for a buying time signifying to members to buy. Obviously when plenty hands make an order for buy much more people in public will also run after the coin, this will shoot price up, volume will rise and the moderators, admins plus few other lucky people sell of then the price crashes. This kind of game continues into another coin. It is just a business with signal groups.
Yes, that have fill their bags way better the announcement on their so called official but private channel. And then they ask all the members to wait for their signal to buy and then boom, they are the one who sells the first taking huge profit. While the people down stream are taking the heat because they don't have the time to sell at the right moment.