The above split frame image demonstrates an object in the terrain out from the Spirit rover brought to my attention
by amateur astronomer Kevin J. Brant wondering what I thought it might be. Now I can't say definitively
what this is, whether a rock or something artificial, but I can say what it looks a little like and is suggestive of.

Note that the left frame is a official size scale view at 100% and then a closer zoom view at 200% on the right.
I have added color to give the scene a more comfortable look. As you can see, if it is a rock, it is very unusual looking
to be that. Not impossible, just improbable. In basic shape it actually looks very suggestive of a Metronome used on
Earth in timing a musical beat as seen in the below fourth image. Note that this Mars object appears to be a hollow
shell adding a bit of emphasis to the artificial Metronome instrument interpretation as a possibility.