This question refers to US Air Carrier procedures for determining takeoff minimums, as published in FAR 91.175, 121.651, Carrier OpSpecs, and the US Terminal Procedures Publication booklet.
As nicely answered in this question, we know that low-visibility minimums for takeoff are outlined in a carrier's opspecs, with paragraph C078 granting approval for "lower than standard" visibility requirements, if the airport runway doesn't already have published higher than standard takeoff minimums.
An airport with a published higher-than-standard minimum for one or more runways is indicated on approach charts with the upside-down triangle with the letter T inside (although this may also indicated only an obstacle departure procedure, or both an ODP and a minimum). The published minimums themselves can be found in the US Terminal Procedures Publication.
My question is about runways marked as "Takeoff Minimum: NA". What does "NA" mean? Does it mean that "lower than standard" minimums may not be used. Or does it mean "all other runways have comments, but no comments are necessary for this runway, so lower-than-standard takeoff minimums published in opspecs are fine and dandy"? There also seems to be different "NA" indications; some with comments such as "obstacle" or "ATC", and some without any comment at all.
I cannot find an answer in the FAA's Instrument Procedures Handbook, the AIM, or elsewhere.
One example is Columbia, CA which has a simple "NA" for runway 35.
Another example is Cloverdale, CA, and RWY 32 is marked as "NA" but has the comment of "Obstacle".
A third example is Merrill Field in Anchorage, Alaska, with the comment of "NA - ATC".