Secret Codes on U.S. Gold Coins?

For some reason, maybe the economy, I have been getting a couple of questions a week from folks asking about the "secret codes" or "special symbols" on U.S. gold coins. The same folks often ask why there is no date on the coin, or mention that the code is where the date should be. They usually want to know if there is any way to tell what year the coin was made. I used to get this question about once a month, but now that it has become increasingly common, I realized it was time to do an FAQ page about it, especially after a friend (who also gets a lot of coin-related questions) told me he was receiving these inquiries too!

So what do these "secret codes" look like? And how can you tell what the date is on a U.S. gold coin when the coin has no date? Look no further than my FAQ about gold coins that apparently have no dates on them.