Hilton wrote:
$ means maintenance required on a METAR (and some people thank that the
FAA has no sense of humor)

The "ASOS User's Guide", http://www.nws.noaa.gov/asos/pdfs/aum-toc.pdf
(linked from http://www.nws.noaa.gov/asos/ ), says that "The $ is used
to indicate that maintenance may be needed but does not necessarily mean
that the data are erroneous." (pg. 2, PDF page 9) Report pages 19, 26,
and 31 (PDF pages 26, 33, and 38) list some conditions under which the $
will appear for problems with various sensors.

Chapter 7 of the AIM tells you how to read a METAR, but doesn't mention
the $ indicator.
http://www.faa.gov/airports_airtraff...7/aim0701.html

Matt Roberds