What do the dollar, plus, brackets and hash symbol indicate in chess moves notations?

Question

I have a doubt about the notations of writing down moves. Also, all these examples are from real games in the database so I don't think the players were analyzing by trying out different moves etc. I would like to understand what these symbols indicate.

Q1: Consider these moves: 1.d4 Nf6 2.c4 e6 3.Nf3 b6 4.g3 Bb4+. What does the + sign at the end of Bb4+ indicate?

Q2: In the following moves 17.Nxg6 Rf7 ( hxg6 18.Qxg6+ Kh8 19.Qh7#) 18.Nxe7+ Qxe7 there is something written inside brackets which seems to indicate move 18 and 19. Also there is a hash sign inside the bracket. But after the bracket is closed, we have move 18 again. What does this indicate?

Q3: In the following example, there is a dollar sign after move 6: 6.Bc4 Be7 $2 7.Qb3 Na5 8.Bxf7+ Kf8. What does these indicate?

Answer 1

Q1: The + means the move gave check to the enemy king.

Q2: The brackets indicate variations. So 17...hxg6 is a variation to the main move 17...Rf7. It starts at move 18 after the closing bracket since then the 17...hxg6 line ends, so it goes back to the main 17...Rf7 variation.

Q3: I was actually unfamiliar with what the $ symbol means before looking it up now. Apparently it's a numeric annotation glyph. Basically a way to briefly write some type of annotation, rather than using English. See: https://en.wikipedia.org/wiki/Numeric_Annotation_Glyphs#main

And for applications of this with chess software: Does anything actually use numeric annotation glyphs (NAGs)?

So for example, $2 means "poor move or mistake", or more simply, the "?" symbol that everyone is familiar with. The reason for using $2 after a move, rather than just adding a "?", seems to be due to issues with representing a pgn file for a computer to understand.