What it is
AASSEP-03 is a NATO Allied Technical Publication that standardises the symbols used to mark an aircraft's servicing, ground-handling, safety/hazard, and armament/ammunition points. Its aim, in the document's own words, is "to standardize servicing markings on aircraft for cross-servicing and to give warnings, the neglect of which may cause damage to equipment or injury to personnel" (clause 1.2). Nations record their agreement to use it in STANAG 3109; that agreement, not AASSEP-03 on its own, is what gives the publication force for a given nation. The current edition is Edition A, Version 1, promulgated in September 2014.
The problem AASSEP-03 solves is interoperability, not aesthetics. When one nation's ground crew services or handles another nation's aircraft under a cross-servicing arrangement, a locally invented symbol for a hazard or a servicing point is worse than useless to a crew that has never seen it before. So the standard fixes a single symbol set, held in five annexes grouped by the kind of point marked: general servicing and maintenance, ground handling, safety and hazard, and armament and ammunition. Clause 2.1.1 requires that markings "shall be in accordance with the symbols and allied data shown and as described in the Annexes", which rules out a manufacturer's own house symbols for these points.
What the requirements cover
Chapter 2 sets requirements for how the markings are formed, located, sized and coloured. Location has one exemption worth knowing: a marking is "not compulsory" wherever there is no possibility the point could be mistaken for anything else. Size is tied to legibility rather than a fixed figure alone: the symbols and inscriptions have to be commensurate with the distance from which they need to be read. Colour follows a convention that differentiates the categories of point, with allowances for camouflaged aircraft, so the marking does not undermine the paint scheme, and for aircraft that may be exposed to atomic flash, where legibility takes priority. The exact dimensions, colour assignments and reflectivity figures are the annexes' own content; a supplier or a maintenance organisation works from the document itself rather than a summary of it.
What is out of scope
The standard is explicit about one exclusion: "Safety markings as applied to rescue are not covered by this standard" (clause 2.3). It also cross-references two non-NATO documents rather than restating their content: ISO 1950, on identifying aircraft servicing, maintenance, ground-handling and safety/hazard points, and ISO 3864, whose Safety Yellow definition AASSEP-03 uses for its own yellow/orange marking.
Who applies it, and how it binds
AASSEP-03 addresses whoever marks and maintains an aircraft: the organisation that builds it, and the maintenance and ground-handling organisations that service it once fielded. It reaches a supplier the way most Allied Technical Publications do, through the STANAG that carries it, and from there through a contract or a type-design requirement that names it. The standard itself names no certification body, notified body, or audit cycle; it does not describe who checks a marking against it or how often. Because what it specifies is a physical feature of the aircraft, checking it in practice falls to whatever quality or airworthiness process a customer or authority already runs.