Letter after the title in roms

[tcg225]

What are the letters and exclamation points after the titles of some roms? Like some have (E) [!] and such.

[Royal Fool]

Those are the GoodROM standards. A [!] means that it is a verified good dump, and the letters such as [E], [U] and [J] represent the ROM's region. ROMs will work differently depending the region they come from, some will work better and some not at all.