I’m not certain how the rules might apply to French Military Operations but there is a general rule about low flying which would certainly impact on non military operations under ICAO in that the safe minimum altitudes are clearly defined. this paper is the US FAA reference that I am familiar with under my US Pilot Licence Commercial Certificate (now out of currency) but widely accepted throughout. In general terms, no aircraft should fly lower than 500 feet or within specified distances of any ground feature, animal or person except when approaching a landing place or in other exceptional circumstances.
It’s no accident that the (civil) aircraft markings size are defined in the ANO so as to be be clearly visible to an observer on the ground within those limits - if you can clearly see the a/c tail number (ie F-ABCD) with normal vision then the aircraft is perhaps within that distance - a bit like being able to read the number plate of a car at a set distance.
A bit difficult at night, I agree and military markings are generally smaller than those required for civil operations - but I defy anyone to read a military jet ident at 500 feet at mach 1+ 
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