Hi Folks,
When I was very young, in grammar school, I was told that the lines around the coin were "evidence of a whole, untampered with coin". Filing around the coin would grind off the lines. Don't take it.
Also, in movies you see old codgers biting the gold coin. That would put their teeth marks on it in case it was stolen, OR, like truckers thump their tires to test pressure, The softness of the gold is indicative of its purity.
Nuns were pretty smart.
Sal