Is there any law prohibiting the attachment of a motor vehicle to a
fixed object while parked in a public street in the City of New York? 
Specifically, would it be legal for me to attach my motorcycle to a
lamp post/street sign/parking meter using a lock and chain, assuming
that I am otherwise obeying
all parking regulations?  If it is illegal, please cite the relevant
New York State/City law.  If you believe it to be legal, please
indicate which sources you have consulted.

Hello robwz!

My research indicates that there is no law forbidding you to lock your
motorcycle to a post, sign, or parking meter, as long as you are
otherwise obeying all laws and your lock arrangement does not "alter,
knock down, cover, remove, or otherwise interfere with" the posts,
signs, or meters.

First, the New York City Traffic Rules and Regulations do not forbid
chaining up your motorcycle:
http://www.nyc.gov/html/dot/pdf/trafrule.pdf

New York State law forbids interference with traffic signs and street
fixtures, but does not forbid attaching bikes or motorcycles to them:
http://caselaw.lp.findlaw.com/nycodes/c128/a48.html

Bike riders routinely chain their bikes to street signs and meter
posts.  Sites discussing bikes reaffirm that it is not illegal to do
so, but caution that police officers have been known to abuse their
broad authority to determine whether such chaining is "interfering"
with public access:

http://www.transalt.org/press/releases/041203abandonedbikes.html
"According to New York State Vehicle and Traffic Law one may not
alter, knock down, cover, remove, or interfere with the operation of
public traffic signals and signs and other street fixtures. It is
against New York City law to lock a bicycle to a tree because the
bicycle and lock could harm and potentially kill the tree; people
should never lock bikes to trees."

http://www.times-up.org/parking_bad.php
"We are expressly permitted to lock our bikes to bike racks, but it is
not illegal for us to lock them to other street furniture so long as
we're not abandoning them or blocking pedestrian or vehicular traffic.
The city has the authority to cut locks and remove bikes if they're
abandoned or obstructing people, but unfortunately this
reasonable-sounding policy is being used as pretext for seizing bikes
that were neither abandoned nor in anyone's way."

So with nothing in the NYC or State traffic regulations forbidding it,
and with bicycles doing so routinely, I think you're probably safe.

Of course, if there's anything else I can assist you with, please
don't hesitate to ask.

Thanks for the answer, and accompanying citations.  It's always harder
to prove that something doesn't exist than to prove that it does. 
This is a fairly thorough review, and matches up with my personal
research.