Also discussed in thread: Shop Talk\Bladesmith Q&A - A Website We All Need To See begun by P. Nap
New York City is a little odd on this. Open carry of a sheathed knife, folder or not, is technically not allowed. However I see a number of electricians, construction workers, and other tradesmen carrying Buck and Shrade folders in sheaths without any problems from the police.
Here's what I found in NYState/City Codes:
Per NYC Administrative Code Paragraph-10-133 and 134:
"It is hereby declared and found that the possession in public places, streets and parks of the city, of large knives is a menace to the public health, peace, safety and welfare of the people of the city;"... and that possession of such knives
"encourages and fosters the commission of crimes".."It is further declared and found that the wearing or carrying of knives in open view in public places while such knives are not being used for a lawful purpose is unnecessary and threatening to the public and should be prohibited".
"It has been found that folding knives with a blade of four (4) inches or more that locks in an open position are designed and used almost exclusively for the purpose of stabbing or the threat thereof."
Basically...
It makes it illegal to carry a knife of over 4" blade length (but NYPD posted at one time in their HQ either "2- or 3-fingers" - guess it depends on how fat your fingers are). Also included is any knife where the blade locks into position and cannot be closed without release mechanism.
Sets lawful possession for military, police, participants in special events (theatrical groups, drill teams, parades), those authorized by Federal Law, EMS technicians on duty, Boy Scouts and Girl Scouts (ok that's an odd choice), or,
"when it is being used for or transported immediately to or from a place where it is used for hunting, fishing, camping, hiking, picnicking or any employment, trade or occupation customarily requiring the use of such knife" or
"a place of purchase or repair" (whereupon it must be wrapped to prevent easy access).
There does appear to be some leeway for legal carry (at least of small knives) but not much.
See the NYC Administrative Code Chapter 1 Title 10 (Public Safety) Paragraphs 133 and 134:
http://public.leginfo.state.ny.us/m...OMMONQUERY=LAWS
Keyword Search: Knives
or
http://public.leginfo.state.ny.us/menugetf.cgi
and go to bottom of page and select "ADC" then go to Chapter 1