if I think personally a safe way to invest in cryptocurrency is :
1. the project runs according to the roadmap and whitepaper that has been made;
2. cryptocurrency that we invest in already has a product;
3. the team always updates about the progress that is happening in the project that we invest;
These points are the quintessential for ICOs. A project fulfilling all three points above is surely going to be successful in long run. Point 1 suggests that everything running according to roadmap which means there is enough buzz about project in the market. It doesn't have to delay its operation due to less response. Point 2 is the best thing an ICO project can achieve,
The actual implication of whitepaper.4. invest in project that are in the top 1-500 in coinmarketpcap (have a high volume);
This is not as relevant as the above three. Some projects restrain themselves from listing on exchanges initially but that doesn't mean such projects are not worth investing. Rather, in my opinion, projects should avoid listing on exchanges before actual execution of project because it will only leads to dumping of coins.
There is no safe investment opportunity. I wouldn't invest in anything that seems suspicous.