I wouldn't try to measure altruism. I would try to set up a system and measure the performance of that system. The social sciences often try to measure people and their "qualities" and it gets very, very difficulty and messy. I see the way forward as building a system and measuring how it performs. Then tweaking it continuously.

A community can have projects. If somebody wanted to know about the community, they would look at the projects pursued by its members. If the goals of the projects are directed towards meeting human needs, then it would be clear to people what that community is about. And they could call the community altruistic, humanitarian or any other word they prefer to use. At the end of the day, it's the goals that matter - and those goals have to be measurable so the people can know if they are meeting them or not.

For example, if I initiated a project about creating a new website on the Steem blockchain, one with educational materials that enables people to both learn and make money, some goals of my project might be to have people successfully complete sections of the content, keep them coming back and going through more and more advanced materials, etc., etc.