It's somewhat uncharted territory, and I am not a lawyer.

But the non-lawyer consensus seems to be that if you're seeking or accepting investment through your ICO, rather than selling something that is useful to your customers and already exists, you are in effect selling an unlicensed security to unaccredited investors, and in the US this is extremely illegal and regulated by the SEC.

You could Google [ICO unlicensed security] to read more about this take.