  Recently, indications for an emission line at 3.55 keV have been found in the
combined spectra of a large number of galaxy clusters and also in Andromeda.
This line could not be identified with any known spectral line. It is tempting
to speculate that it has its origin in the decay of a particle contributing all
or part of the dark matter. In this note we want to point out that axion-like
particles being all or part of the dark matter are an ideal candidate to
produce such a feature. More importantly the parameter values necessary are
quite feasible in extensions of the Standard Model based on string theory and
could be linked up to a variety of other intriguing phenomena, which also
potentially allow for new tests of this speculation.
