2006 New York Code - Labeling Gas Vents.

 
    §  27-885  Labeling  gas  vents.  Gas  vents  for  use  with gas-fired
  equipment, and which are not designed  for  use  with  solid  or  liquid
  fuel-fired  equipment,  shall be plainly and permanently identified by a
  metal label etched or embossed to read: "This gas vent is for  equipment
  which  burns  gas only. Do not connect to incinerator or solid or liquid
  fuel-burning equipment." This label shall be attached to the vent  at  a
  point  near  where  the  gas  vent  system  enters the wall, ceiling, or
  chimney.