John L. Sorenson argues that the Nephites did not have coins but instead they had weights.
John L. Sorenson, "Anthropological Approaches of the Book of Mormon," Book of Mormon Institute, December 5, 1959, ed. Dee F. Green (Provo, UT: Book of Mormon Institute, 1964), 26, M222 B855b 1964 no. 2, Church History Library
I would say the specific kinds of proof that we have been seeking for are at least likely to be found. If we look to the Bible, as an example, we see that the same methods that we have used to seek proof for the Book of Mormon have been used much longer to seek proof for the Bible. What has been the result? Practically speaking, there are only a handful of specific proofs of the Bible and most of these, or perhaps all of them, are in question. If we find a particular wall that might have been built by David, how can we know it was built by David? Maybe it was built by Saul, or maybe it was built by the Canaanites, or maybe it was built by the Persians, long before David, and almost never can we be really confident. How can you be sure of the identification of specific things? What we do know is that a wall was built, or, more importantly, that walls were built. For example, can we expect to locate Nephite coins as "proof" of their presence? The answer is no. In the first place the Book of Mormon, thank goodness, never mentions coins--only money. ("Coins of the Nephites" occurs only in a chapter heading inserted in the course of publishing the scripture.) Coins were not in use in Palestine for generations after Lehi departed; the Old Testament "shekel" was a weight unit for measuring money, not a coin, and the Nephite money was almost certainly the same. No authentic "coin" has ever been found in America under convincing circumstances, and some reported finds can be shown to be either fakes or otherwise unbelievable. Here, then, is another "specific" shoal for us to crack up on. In fact, the lack of coins is precisely what we should expect if the Nephites came from Palestine very near 600 B. C.