So we see from this articles that SEC consider almost all crypto currencies as securities - i suggest all who are interested further into this topic, that you read them.
The SEC mostly seems to be interested in 'tokens' and not cryptocurrencies in general. They have been very clear, for example, that Bitcoin is not a security.
Some of the stronger indicators of a security are:
1. that the token receives a dividend or part of the profit share of the organization.
2. that the token entitles you to rights should the organization close down and the remainder of funds are distributed to all the token holders.
3. holders of tokens can vote in matters of the orgnaization
None of these indicators are true for Stratis which counts strongly in favor of Stratis being a utility coin. If there are any other more obscure arguments towards a security it would be weak arguments. Stratis will be used to do stuff on the Stratis platform e.g. to pay for creating sidechains or other use cases where it becomes "fuel" or just in general to pay for stuff which counts strongly in favor of being a utility coin.