- In the XMB, go to either Game, Music, Video or Photo.
- Press triangle to bring up a menu, then click "Information".
- If the MagicGate text says "compatible", then it's a genuine memory stick. If it says "Unknown", it's most likely a fake (at least it's not MagicGate compatible).
Mine says "Unknown", which doesn't really surprise me as I bought it cheap from a stand in town. It's working very well, though, maybe a little slower than a genuine, so I guess I'm lucky.
What about your memory sticks, are they genuine?
Thanks to Muratcan.