Your housing has been hand-polished using buffing wheels in successive grits from a raw machined surface up to a mirror finish (up to the level that a reflection can clearly be seen in the surface). However, please note that, because of the mechanics of using a round wheel to polish a flat surface, there will always be some microscopic patterns visible on any mirror-polished stainless surface if you look at it at certain angles under bright light. Once you start to use the part and have a fingerprints on it, you likely won’t notice these any longer.
For everyday maintenance of the part, you can use a simple microfiber cloth to wipe away fingerprints (though I always recommend not stressing about that or it’ll drive you crazy; fingerprints shouldn’t harm the steel). If, over time, you find areas of the part becoming dull, you can carefully buff the part with Simichrome polish.
If you get a more significant scratch or other areas of wear, you can always send the part to a local metal polishing shop (we recommend General Brite in Los Angeles). The beauty of an uncoated finish like this is that it can be repeatedly re-finished in this way and thus is maintainable over time.