PA-john, be careful with the enticing logic of "the iron signal that turned out to be a lunchbox full of coins", blah blah.
The same thing/logic could be said of "a foil signal in a blighted urban park that turned out to be a diamond ring", etc...
On the surface, each of the illistrations above would seem to be fool-proof that you should 1) dig everything, even iron, because .... afterall, you never know if it's not an iron container of goodies, or iron masking something, etc..., 2) dig all foil, no matter how flitty and junky sounding, and no matter how junky/blighted a spot you are working, because afterall, gold jewelry shares foil range TIDs.
Here's the problem with this: Let's say you are playing blackjack in Las Vegas. You have 20 in your hand. Do you "take another hit", or do you "hold"? Of course you HOLD, right? But why? How do you KNOW that the dealer *might not* deal you a 1 card on his next deal? Afterall, you *might* loose the hand if the dealer has 21 in his hand, so SHOULDN'T you take another hit just to be sure?
You see, it's all in the odds: I can go dig 1000 large iron signals in an urban demolition site, or on the beach, or wherever, and odds are ...... 1000 of them will be just that: large iron. Sure, once in awhile there'll be a conductive item that was being masked, or better yet, once in awhile you hear of an iron box filled with something. But the trouble is, you will loose the black-jack analogy, because you will have merely driven yourself mad, in the preceeding 1000 digs or whatever.
And for the foil/small gold analogy, (beaches excepted), I once hunted with a fellow who considered it fool-hearty to pass any little teensy foil, "lest he miss a gold ring". Well this fellow was seeing me come in with some barbers and such from a certain park, so I took him with me one day. He figured he could "have the best of both worlds" (old coins and turf jewelry both), by "digging all". He lasted about 30 minutes, and finally got to "cherry picking" a little, when he realized he was never going to get out of a circle 10 ft. square, and would likely get us both kicked out of the park d/t several holes every foot.
I know this sounds horrifying to some types hunters, like some hardcore CW hunters, who do indeed even dig the nails and such, or beach hunters, who have no trouble with the occasional beach nails, etc.... But other land and turf hunters will know what I'm talking about. Sometimes the person who "comes in at the end of the day" with the nicest picks, is the person who didn't spend all day digging trash & iron. Sometimes it simply isn't possible to "have it both ways".