I think that best way is going to check how the ICO is publishing itself.
If they are doing it by publishing the project then we are good, but if they do so by publishing how much money the investors can make from investing in the project- it shows that they are really greedy and shouldn't be trusted.
On the other hand- a also very storng indicator to consider is the devlopment team, if the team is unable to show a record that they were able to go out with simillar products or that they really have the ability to finish the project then I wouldn't invest in them either.
If the team is unable to finish the project your investment will probably ended up as a loss.