To calculate the signature of an input video and store it in signature.bin:

ffmpeg -i input.mkv -vf signature=filename=signature.bin -map 0:v -f null -

To detect whether two videos match and store the signatures in XML format in signature0.xml and signature1.xml:

ffmpeg -i input1.mkv -i input2.mkv -filter_complex "[0:v][1:v] signature=nb_inputs=2:detectmode=full:format=xml:filename=signature%d.xml" -map :v -f null -