The assay office (aka Office of the Assayer) was a facility located on the Promenade of Deep Space 9 and used for the storage of valuable items.
The most secure location on the station, each storage locker in the assay office was surrounded on all sides by individual force fields. The locks could only be opened using a personal authorization code combined with a verified retinal scan. The retinal scanners were Cardassian-made MK-12 models, with L-90 enhanced resolution filters.
In 2369, dubious archaeologist Vash used the assay office to store valuable artifacts collected during her time in the Gamma Quadrant. (DS9: "Q-Less")
Freyla worked in the assay office in 2370. (DS9: "Shadowplay")
Trelos Vren was once arrested for trying to break into the assay office sometime prior to 2372. (DS9: "Indiscretion")
In 2373, Arissa broke into the assay office in order to steal a data crystal formerly belonging to Tauvid Rem. She was stopped by Odo. (DS9: "A Simple Investigation")
Michael Eddington's possessions were stored in the assay office after he defected to the Maquis. Among the items was his lucky "looney". (DS9: "Blaze of Glory")
Morn kept a brick of gold-pressed latinum in storage locker 137 in the assay office, which was "inherited" by Quark after Morn faked his own death in 2374. The brick came from the haul of 1,000 bricks stolen by Morn and his accomplices during the Lissepian Mother's Day Heist, and was inscribed with the number of an account in the Bank of Bolias, in which was deposited the rest of the money. (DS9: "Who Mourns for Morn?")
The assay office's logo was seen on an interface that Arissa used to gain access to the facility, and also on the doors to the office itself. A list of names of other people who were storing valuable items in the assay office during that time was legible on a viewscreen. Some of the names make sense, others are nonsensical. The following names were visible: Define Having, Deflate Release, Deo Thermometric, Elbow Grease, Either Oneorother, Fiscal Vertebrate, Cold Fusion, Hydro Carbon, Hungry Weakness, Lachrymose, Intramural Baby, Lactic Acid, Lourenco Marques, Love Seat, Masora, Mass Commun, Chiefly Moulding, Molly Coodle, Nilo Saharan, Nimrod, Pusan Korea, Jerry Maguire, Rhyme Orreason, Olivia Eaves, Alicia Eaves, Sister Hood, Synchro Nized, Treble Clef, and Tauvid Rem.