Recently, David Fitch has put forth the idea that localized faith communities of the more organic/unofficial variety should consider manifesting themselves politically if they truly wish to be a visible presence to the culture surrounding them. It's an interesting read, and before we go much further I'd suggest you give it a thorough read yourself here...
The thing is, I don't really feel all that confident in David's advice to "make it official."
Just because political bodies are more readily "visible" to the culture around us, I don't believe they are necessarily the best way for the Church to draw attention to God's mission.
If not solely for the fact that Jesus resisted the partisan route Himself, I'd argue politicizing your community leans a bit more toward "of" than "in," and I'm not sure how helpful that is in a world where politics often seeks (and finds) its power through division.
Writing from within the context of a Church community with a 125 year history as a political body already I would argue the greater witness of the North American Church (politicized or not) is on its best display when we partner with the political bodies in our midst already (city councils, parent teacher associations, etc) and work for the Kingdom therein; subverting even while supporting, and ever mindful that our participation within these bodies introduces Jesus to those already inspired to work alongside each other by an "unknown god."
In particular, at Hillside I'm fascinated by the challenge to take a politicized-body-with-minimal-political-clout and encourage our members to engage their neighbour on a personal level; to manifest the Kingdom around our dinner tables and on our soccer fields, to weave Christ throughout the fabric of our civic lives.
If the personal is political I'm arguing we need a real dose of personality.