In reply to Jragon:
>"So if a grade is 6a it's a sport, whereas if it's HS it is a trad route?"
Yip.
Sport = 6a (on this site but more frequently it's prefixed with a capital "F", for French, i.e. F6a (note: lower case "a" rather than upper case, most frequently used for sport)
Trad = HS 4a (HS = Hard Severe, 4a = British technical difficulty)
Bouldering = f6A (on this site but more frequently it's prefixed with "font" (for fontainebleu) rather than just the lower case "f" ie, font6A (note: upper case A rather than lower case, often used for bouldering)
V2, V3 etc. is also bouldering
See St.Bees for an example of a crag with all four grading systems in use...
http://www.ukclimbing.com/logbook/crag.php?id=769