The Globe's website, Boston.com, has an article today about Somerville that mentions "the polyamorous meetup every Tuesday at the Diesel Café":
...with a link to the main Poly Boston website.
If they call it a "meetup," they may have found it by looking up the Meetup.com groups in Somerville. This is a reminder that the Diesel gatherings are listed for the public as official Meetup.com meetups. These are expected to have a host who welcomes newcomers and supposedly runs things. This is what newbies who come to the Diesel from Meetup.com probably expect; after all, they were invited.
So if you notice a stranger who shows up looking like s/he is looking for a group, it really would be nice to say hello and ask if they came for Poly Boston. Either that, or take the listing off Meetup.com.