2013-02-11
No. Anything created by a person in the USA is automatically copyrighted and thus proprietary by law. If said person abandons it, or even dies, it remains copyrighted by them for 95 more years (at least). Public domain, or any other terms relaxing legal copyright must be directly, clearly, and precisely declared. This is why we have "BSD Games" and "BSD Games non-free" in stead of a single package. The non-free games were implied to be free (as in scientific knowledge for the good of all mankind), but the authors (of _most_ of the 'non-free' games) didn't declare any legally binding terms before dying.

International law/Berne convention is slightly more relaxed but the same principle applies.

2013-02-11 (updated 2013-02-12)
No. Anything created by a person in the USA is automatically copyrighted and thus proprietary by law.

Sure, but the do as you wish thing attached with it essentially relinquishes that. If that doesn't work, then I find the process to actually make something public domain strangely difficult.

Edit: this pretty much makes it the author forfeited their copyright on the material, making it public domain.
Edit 2: More difficult methods seem to only apply to works that were registered: www.publicdomainsherpa.com/no-rights-reserved.html
What should you look for, then?
What you want to see, basically, is unequivocal language acknowledging that the author is giving up all rights in the work ... and allowing you (and everyone else) to do whatever you want with it.

2013-02-12
That's all well and good until some lawyer says "Your Honor, surely the defendant is not implying that the author was advocating that people should violate the law. Clearly he meant 'do as you wish' within copyright law." It most be more than clear, it must precisely relinquish rights.