Being an avid detectorist (surely there has to be a cooler name for someone who Metal Detects as a hobby…), I have a serious love/hate relationship with nails (not my nails – metal nails that attach wood to wood, though my nails are pretty beat up at the end of a hunt!)
The ubiquitous wire nail seriously detracts searches of property in the modern (post 1900) era.
My detecting area of interest is pre-1800 pioneer settlement of the central Annapolis Valley (Wilmot and Aylesford Township, eastern Annapolis and Granville Townships). There is nothing more interesting (to me..) than starting a search of an area that looks like it was previously modified by human activity (straight tree lines, leveled ground, evidence of stone walls) and hearing the low grunt of the machine registering a wrought iron signature (4-5 on my Fischer).
The discovery of a hand-wrought nail (squared with a rose-head top) tells me I am in the right spot. The nail, in and of itself, is evidence of high probability pre-1800 human activity. Of course, there will be other evidence that must be found to prove the timeline I am studying as the hand wrought nails were likely used in NS into the early 1800s.
Due to the acidic soil nature in my area of study, wrought nails are usually seriously degraded, almost to the point of crumbling when I find them. I actually am happier finding an intact rose-head than when I find a copper penny.
Anecdotally, I have hear that several pioneer settlers would burn down old buildings to salvage the square nails, as they were tremendously expensive. This seems plausible.