The two most common markings are "
Outside Type" and "
Wall Mount Only", often a website description will indicate the latter but when you pull up the actual mfgr's instructions it says "Eave or wall mount"
Eave mount? Or Soffit mount? Sometimes the unit is designed so that the sensor and lights cannot be angled appropriately when installed in an under-eave location, either they won't angle sufficiently, or light bouncing off the eaves will trigger the daylight sensor and turn the security lights into rave lights.
Looking at the referenced unit, you can see how the lights and sensors would point poorly if mounted under eaves:
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