I didn't log in. For almost all of these they detect that I'm connecting from my campus IP block and unlock everything.
Distinguished editors strap Finster into vacuum target chamber...
"Come now, editorial board of Nature. Do you expect me to pay for a subscription?"
"No, Mr. Finster -- we expect you to fuse!"
I accessed over a vpn link into campus, signed-in by my user ID. The md5sum of the link provided above (and the others in the thread) are identical to the copy I downloaded from my campus IP block. Unless you're also on the campus of Iowa State, I don't think they're watermarking this paper.