The fact that the mint mark sits in a depression in the coin is typically a red flag that a coin might have an added mint mark. On this coin it is one of the diagnostics used to authenticate it.
Not so sure about that. Many of the genuine ones I have handled over the years appeared to have a mintmark in a depression. I have found that the ones that have perfect looking mintmarks are much more likely to be added and the "blob"-like mintmarks that appear to be set in the depression are the genuine ones.
If you reread Mike's post, sir, I believe you'll find you're on the same page. His first sentence reads as a general statement, while his second addresses the issue in question. That said, I don't see anything suggesting the coin likely fake, but this doesn't mean it should be deemed real because of it. Considering what the OP has said thus far, submitting is likely foolish (for him), so if he's intent on taking it to this show, all that remains to be seen is if he wishes to post the requested photos and possibly get a better understanding of what he has before attending.