Who cares? There is no WKC in http://pets.groups.yahoo.com/group/The_GSD_Source/links/Kennel_Clubs_001198303430/ and so whatever you have come across has no credibility anywhere in the world so far as dogs are concerned. It is presumably yet another scam-artist outfit in the USofA.
I came to your question expecting you to be asking about F1, F2, F3 etc or P1, P2, P3 etc. Or possibly about "Linebred 2 : 5,4" or similar.
In most of the world, # stands for "number", so #6 ought to mean "number 6" - maybe the 6th pup in a litter.
But Yanks seem to use it to stand for "pound", so 6# would mean that that pooch weighs 6 pounds.
However, the AKC's definition of that breed: http://www.akc.org/breeds/toy_fox_terrier/ includes neither # nor 6
But this http://www.nzkc.org.nz/br120.html breed (known as rat terriers in the USofA) is expected to be in the weight range 6-to-8 pounds.
A third possibility occurs to me - maybe you are looking at a show catalogue for a district club such as a Washington KC or a Winnipeg KC? In which case it is the bib-number (or arm-band-number, or chest-card-number) to be worn by the dog's HANDLER during that class. Alternatively, you could be looking at that club's results sheet, and that particular terrier was 6th in his/her class.
Your question simply does NOT give us enough information for us to know what context applies to that "#6".f.
If [cmspotts..] is correct about bib-numbers 1 to 4, we have yet another example of "Only in America" lunacy!
[Horse Lover]: I have NO interest in Westminster - none of my breed are shown there, because the judges aren't used to seeing actual GSDs that fit the International Standard of the GSD and have passed a Breed Survey. Those judges don't even know how the GSD is supposed to STAND, despite that it is carefully drawn as http://www.gsdca.org/Noframes/standard/Illo22.htm in the GSDCAmerica's rebel "Standard" that is ALLEGEDLY used by the AKC.
I personally dumped the all-breeds scene in January 1976, although I had been very active before that as exhibitor and as judge's steward, and in 1975 had been show treasurer for our equivalent of Westminster.
Les P, owner of GSD_Friendly: http://pets.groups.yahoo.com/group/GSD_Friendly
"In GSDs" as of 1967