We identify a weak line at 3.5 keV in X-ray spectra of the Andromeda galaxy and Perseus galaxy cluster using deep exposures from the XMM-Newton Telescope Science Archive. The detection of this signal is presented, along with evidence that it can not concern a previously unknown systematic. The possibility is discussed that the signal originates from the decay of dark matter particles rather than an astrophysical source. Finally, outlines of ongoing and future work to test this scenario are given.