In Stories in Stone, Douglas Keister doesn’t provide a lot of specific information about the symbolism of the lyre. Music overall is noted as being “associated with reverence,” and the lyre is mentioned as being considered a more playful instrument and associated with Apollo. Other sources that attempt to explain funerary symbolism suggest that many depictions of the lyre in cemeteries show a broken string to symbolize the end of life. Of course, it could just be marking the grave of a musician.
A Grave Concern 