I have an Arduino Mega ADK which doesn't have a 501K but has 504C Component. Now is my Arduino Fake??? :o :o :o
I think you are looking at the 500mA polyfuses for the two USB connectors. The official pictures show "500Z" on the older model and "501L" on the Rev 3 so I don't think you can tell from that part. Perhaps if you could add well-focused and high resolution images of both sides of the board someone might be able to tell you if you have a counterfeit or not.
What color are they? The real ones are like, brownish, like the pictures show - but the vast majority of fakes are green (that's the most common color for polyfuses).
Note that fakes, like clones, typically work fine.