In my own opinion there is no specific way how to determine if the ico you like is legit or not scam because we will only know it if the ico is already finished but i have my own way of determining if i can trust the ico first is I'm looking who is the bounty manager of that specific ico and i will search some information about that ico.
There are too many factors on how to check whether that ICO is legitimate of scam but for me, I can spot them just buying on their Telegram Channels because I do believe that good ICOs have a very strong social communities like Telegram, facebook, Twitter etc.
check the number of social participants like Telegram, they should have more than a thousand active members and admins are available at anytime of the day because good ICOs do have social managers and moderators.
otherwise, that ICO has a higher chance of being a scam or bogus.