Not all crypto signal groups are bad, they are all created by scammers. There are still lots of groups that are helpful and share knowledge as well as share some signals to refer to together. But those groups only operate privately with some close members, not sharing to the outside like other scam groups, you can't find those groups unless you know someone.
The best way is to do your own research and find out, relying on others is also not a good thing because we cannot be sure that they will always be right.
Perhaps you are right. But imagining finding 1 legit telegram group out of 100 groups, you can just think that I was waste of time. And instead of doing this, I'd rather spend my time doing research, familiarizing the market, and much more taking time for technical analysis as I know these are the things needed to have a profitable trade, not on relying others.
Because if we are just aware how scam is rampant in telegram, I believe nobody will even have to trust any from them, in those who says are experts.