Warning flags - also known as truck flags or warning markings - on tail lifts are intended to prevent other road users from overlooking the moving platforms on the lorry and causing accidents. As visibility should be guaranteed, especially in the dark and in poor lighting conditions, 
warning flags | must be fitted with a reflective film (see extract from the German StVZO - Road Traffic Licensing Regulations below).
Attention, warning flags for tail lifts in the colours red-yellow (fluorescent yellow, fluor-lime) are intended for fire brigade emergency vehicles and are only permitted with 
special exemption (according to § 70 StVZO , in accordance with DIN 14502-3).
In addition to reflectivity, other performance criteria of the flag are durability, durability and flexibility. This is where the products differ considerably.
The warning flags can be attached to the tail lifts using mounting rails.
§ 53b StVZO (excerpt, translated)
(5) Tail lifts and similar devices, except those on buses and coaches, must be identified during operation by two flashing amber lights with a luminous intensity of not less than 50 cd and not more than 200 cd and with clearly visible red and white warning markings. The flashing lights and the warning markings must - in relation to the working position of the equipment - be mounted at the rear end if possible and as far to the outside as possible. […] The red and white warning markings must be retroreflective and need only be effective to the rear. In the case of vehicles on which permanently mounted flashing lights are incompatible with the intended use or the design of the tail lift and in the case of vehicles on which retrofitting is not possible with reasonable effort, at least one portable flashing light must be carried, installed and operated appropriately as a safety device for tail lifts or similar equipment.
Source: Quelle: https://www.gesetze-im-internet.de/stvzo_2012/__53b.html
