As a quick experiment, I put some baking soda in a shallow dish, and shook it a bit to randomize the surface. I then pressed a Phillips Head screw into it.
Here is another impression, with the screw that made it next to it:
As much as I would like this to be a "fossil", I really think it is not.
The problem with the Phillips screw imprint in the nasa image is that it is not "quite" a perfect screw head imprint. So I began to look at tamper-proof Phillip screw images online. One thing led to another and I arrived at this photo of an Alpha particle X-ray spectrometer from a NASA rover. I think you will be impressed!
http://commons.m.wikimedia.org/wiki/File:MER_APXS_PIA05113.jpg
