If it's a real HK receiver, there's a 99.9% chance it's a real HK barrel. Barrel replacement on an HK is an extremely time-consuming ordeal (i.e. expensive), and the barrel itself probably costs less than the labor to replace it.
Anywyas, from the HKPro home page, world of hk, here's info on the symbols on HKs:
You may also see a tiny sort of circular or diamond shaped stamp, it's the Nitro Eagle. Many times there is a "js" on the base of the barrel as well.