Hmm, well... I have always understood it so that: (a) yes, it's GPL-2 (what else could it be) and (b) it means that the restrictions of GPL apply insofar as they make sense, e.g., you can pick it apart and reuse it in other GPL-2 or compatible products, but not take it proprietary. Upon request, distributors should probably be prepared to deliver a machine-readable version of the source code. However, there is no requirement of attribution, as with some of the CC licenses.
By and large, I think this makes sense for technical documentation files. E.g., the help file for poisson.test has stretches of text copied verbatim from binom.test, and it would be ridiculous if such cross-pollination would require that Peter, the author of poisson.test should put in a statement that some of the text was borrowed from binom.test, by Kurt. (In this particular case, both are (c) R Foundation, but you get the point.)
For more extensive free-standing documents, there might be a point in using a CC/FDL-style license instead. However, these licenses appear to be GPL INcompatible, so some care is required. ?Until now, the GPL plus Common Courtesy has worked well enough.