To dream of an urn represents permanent changes or losses that you feel good not having to let go of for good. Feeling good keeping a memory or impossible idea alive in spirit. It may also reflect remembering how good your failed hopes or plans could have been.
Alternatively, you or someone else may have undergone a difficult change and keep holding on to the past in whatever way they can.
To dream of the contents of an urn not being ashes reflects the manner in which you are choosing to keep the spirit of something lost alive.
Example: A woman dreamed of digging up a grave to find an urn with pepper in it. She felt good about the pepper. In waking life she was discussing a dead lover with love ones after a long time of not doing so. She felt that discussing his life was a good thing to keep his spirit alive as long as the discussion was moderate.