FOR six years or so one of the more astonishing sights of New York has been the graffiti on the subway trains. The word “graffiti” scarcely suggests, to those who have not seen them, the enormous graphics which decorate the sides of subway cars-murals which march relentlessly over doors and windows, and which may incorporate successive cars to provide the graffiti maker a larger surface on which to paint. They are multicolored, and very difficult to read, but they all, in one way or another, simply represent names. There are no “messages” -no words aside from names, or rather simplified and reduced names, nicknames, or indeed professional names, often with a number attached.  (One will not see an Alfredo, Norman, or Patrick, but Taki 137, Kid 56, Nean.) There are no political messages or references to sex-the two chief topics of traditional graffiti. Nor are there any personal messages, or cries of distress, or offers of aid. There are just large billboard-type presentations of the names of the graffiti-makers, in an elaborate script which, with its typical balloon shapes, covers as much surface as possible.