Silver,
I don't know about the F-75, but the M6 loves gold jewelry.
Put your DISC to about 9 o'clock, just above nails. You'll pick up any 10k, 14k, 18k necklaces and bracelets that are there. I've found rings, necklaces, one bracelet and of course silver with it set that way. What I normally do with the M6 is set the DISC there, then turn on Tone ID by pushing the trigger forward and leaving it there. I listen for high tones and for low tones, if the middle tones are brief and repeatable then I'll dig those too although lots of trash can fool you. Usually bracelets and necklaces will come in as a low tone and the silver/clad/copper will come in as the highest tone.
If you run across a hard hitting odd shape object it could be jewelry. The M6 does hit hard on 14k gold and 18k gold. I've never found anything 10k but only because it wasn't in the ground or the sand where I was detecting.