Legal ICOs do not exist at this time due to lack of regulations and due to absence of any law to guide it. The legal community and the Blockchain community are discussing the issue to death and somehow, the simple way forward is being missed - Self-Regulate.
Most of the exchanges that are coming up with a legal ICO are doing exactly this - self-regulating. None of the exchanges have the legal right to regulate a business - the best they can do is either allow or disallow trading as a measure of control. Exchanges like Polymath and OiX have even laid down their own guidelines for an token to be listed on their platform. In such a scenario we are gettign a clearer picture of what Legal ICo might look like in days to come or for that matter how the Legal ICO looks right now.
This community is being maintained by the folks here at oix.global. OiX (Open Investment Exchange) is coming up with a Legal ICO standard whihc they have tentatively titled Initial Securities Offering. More about it can be found in the forum. We would also encourage you to discuss on other standards such as Securities Token Offering, which according to us is also a step in the right direction.