What does (U), (J) and [!] mean in my roms?

STANDARD CODES
[a] Alternate
[p] Pirate     
[b ] Bad Dump
[t] Trained          
[f] Fixed
[T] Translation       
[h] Hack
(-) Unknown Year       
[o] Overdump
[!] Verified Good Dump
(M#) Multilanguage (# of Languages)          
(###) Checksum
(??k) ROM Size         
ZZZ_ Unclassified
(Unl) Unlicensed     

COUNTRY CODES 
                                               
(1) Japan & Korea
(4) USA & Brazil NTSC 
(A) Australia
(J) Japan            
(B) non USA (Genesis)
(K) Korea            
(C) China
(NL) Netherlands      
(E) Europe
(PD) Public Domain    
(F) France
(S) Spain            
(F) World (Genesis)                         
(FC) French Canadian
(SW) Sweden           
(FN) Finland
(U) USA             
(G) Germany
(UK) England          
(GR) Greece
(Unk) Unknown Country  
(HK) Hong Kong
(I) Italy      
(H)  Holland
(Unl) Unlicensed      

STANDARD CODE NOTES
                                              
[a] This is simply an alternate version of a  
      ROM. Many games have been re-released to  
      fix bugs or even to eliminate Game Genie  
      codes (Yes, Nintendo hates that device). 
[b ] A bad dump often occurs with an older     
     game or a faulty dumper (bad connection). 
     Another common source of ROMs is a   
     corrupted upload to a release.       
          
[f] A fixed game has been altered in some way
     so that it will run better on a copier    
     or emulator.                              
           
[h] Something in this ROM is not quite as it  
     should be. Often a hacked ROM simply has  
     a changed header or has been enabled to   
     run in different regions. Other times it  
     could be a release group intro, or just   
     some kind of cheating or funny hack.   
[o] An overdumped ROM image has more data     
     than is actually in the cart. The extra   
     information means nothing and is removed  
     from the true image.                      
                           
[t] A trainer is special code which executes  
     before the game is begun. It allows you   
     to access cheats from a menu.  
 
[!] Verified good dump.