I live in an urban neighborhood that was built around the same time as the S neighborhood. We do not have a HOA, but we do have a Neighborhood Association, and so do the other neighborhoods around us. We pay voluntary annual dues, and those dues go to things like landscaping, rental of the park clubhouse for parties, and other things that our elected leadership deem to be for the good of the neighborhood. They do things like advocate for traffic lights at dangerous intersections, get word out when there is a city council vote on an issue that impacts us, attend council meetings, and provide input. Our neighborhood association spends a lot of time on advocating with LE to make sure we have good coverage and are informed about break-ins and the like (Police have a liason assigned to each neighborhood association). We do not have a private security force, but if we did, we would pay for it out of our dues.
When a crime occurs -- there has only been one murder in the last 15 years, but there are plenty of thefts -- the association is very active in getting and disseminating information and in trying to get word out for witnesses to contact LE, etc. Most of this is done over email.
I don't know if the S neighborhood had something similar, but I would be a little surprised if not.
ETA:
http://www.wpcaonline.org
The S. house is outside the boundaries of the Woodley Park Community Association. I remember some discussion of a second neighborhood that their house was a part of, but can't remember the name. I suspect that neighborhood has a community association as well.
ETA 2: Maybe it was Cleveland Park:
http://www.cpcadc.org