There are several on the south eastern side of the Anacostia. The Naval research labs has a couple, the Secret Service has a couple. The ones on Hummers are mostly Avengers (basically two four packs of stinger missiles) the others are NASAMS (a Norwegian anti-aircraft missile system) for all the money the US spends on weapons, we don’t have a natively developed SAM capability, so we use the Norwegian system to defend our capital. If you look closely, you can sometimes see Avenger systems scattered around town. I know the Naval Observatory has them, there are at least two on rooftops near the White House.