/usr/share/octave/4.2.2/m/signal/ is in octave-common 4.2.2-1ubuntu1.
This file is owned by root:root, with mode 0o755.
..
/usr/share/octave/4.2.2/m/signal/arch_fit.m
/usr/share/octave/4.2.2/m/signal/arch_rnd.m
/usr/share/octave/4.2.2/m/signal/arch_test.m
/usr/share/octave/4.2.2/m/signal/arma_rnd.m
/usr/share/octave/4.2.2/m/signal/autoreg_matrix.m
/usr/share/octave/4.2.2/m/signal/bartlett.m
/usr/share/octave/4.2.2/m/signal/blackman.m
/usr/share/octave/4.2.2/m/signal/detrend.m
/usr/share/octave/4.2.2/m/signal/diffpara.m
/usr/share/octave/4.2.2/m/signal/durbinlevinson.m
/usr/share/octave/4.2.2/m/signal/fftconv.m
/usr/share/octave/4.2.2/m/signal/fftfilt.m
/usr/share/octave/4.2.2/m/signal/fftshift.m
/usr/share/octave/4.2.2/m/signal/filter2.m
/usr/share/octave/4.2.2/m/signal/fractdiff.m
/usr/share/octave/4.2.2/m/signal/freqz.m
/usr/share/octave/4.2.2/m/signal/freqz_plot.m
/usr/share/octave/4.2.2/m/signal/hamming.m
/usr/share/octave/4.2.2/m/signal/hanning.m
/usr/share/octave/4.2.2/m/signal/hurst.m
/usr/share/octave/4.2.2/m/signal/ifftshift.m
/usr/share/octave/4.2.2/m/signal/periodogram.m
/usr/share/octave/4.2.2/m/signal/private/
/usr/share/octave/4.2.2/m/signal/private/rectangle_lw.m
/usr/share/octave/4.2.2/m/signal/private/rectangle_sw.m
/usr/share/octave/4.2.2/m/signal/private/triangle_lw.m
/usr/share/octave/4.2.2/m/signal/private/triangle_sw.m
/usr/share/octave/4.2.2/m/signal/sinc.m
/usr/share/octave/4.2.2/m/signal/sinetone.m
/usr/share/octave/4.2.2/m/signal/sinewave.m
/usr/share/octave/4.2.2/m/signal/spectral_adf.m
/usr/share/octave/4.2.2/m/signal/spectral_xdf.m
/usr/share/octave/4.2.2/m/signal/spencer.m
/usr/share/octave/4.2.2/m/signal/stft.m
/usr/share/octave/4.2.2/m/signal/synthesis.m
/usr/share/octave/4.2.2/m/signal/unwrap.m
/usr/share/octave/4.2.2/m/signal/yulewalker.m