ADCO was a department, division, or position within Starfleet's Fleet Operations Center on Earth. (ENT: "Demons" set artwork)
In January of 2155, Starfleet officers J. Rudolph, J. Mees, M. Westmore, J. McMeikan, D. Curry, and M. Gullesserian worked in (or as) ADCO.
ADCO was seen on directory listings seen on the set of "Demons".
, like many of the other divisions, departments, or positions on the listing, is a reference to NASA
terminology, in this case, the "Attitude Determination and Control Officer".