First you need to know that scams do not come to you and catch you. Obviously you go to them so proper way to avoid them is too know them clearly. There are some signs that will give you hints about is it legit or not. Like proper presentation of the project, solid whitepaper, renowned team members, good ico and bounty managers etc are the sign of good Altcoins.
I totally agree with you. The signs are written all over the wall, it's just left for us to spot them using various parameters. like:
1. Public Team
2. if the amount they intend to raise is not too much for what they intend to achieve
3. Do they have a prototype
4. is the project too ambitious
5. Solid team