If you read it, it’s true. If you hear it, it’s magnetic.
All charts and textual sources such as the METAR, TAF, winds aloft, surface analysis charts, etc. use true north as the reference.
ATIS broadcasts, or any information a controller gives you over the radio, is magnetic. From the AIM, “Wind direction broadcast over FAA radios is in reference to magnetic north.”
References:
1. AIM Section 7-1-11 page 7-1-26 in the 5/26/16 edition.
