I hate the small "dept of transportation" logos on every sign, especially the big green highway ones. They look better without them.
From a collector's point of view, I think that label helps identify it as a genuine New York City sign and differentiates it from others manufactured for other municipalities in the country.
Just my two cents.
Lowers the resale value. Seriously. If someone tries to sell it, the logo gives it away as a stolen sign.
I would have to disagree with you on that to some extent. It depends on what the sign is and how valuable it may be to a collector. Some that have the old
"DEPARTMENT OF TRAFFIC" labels (pre-1977) sell for more than others that are fairly newer. I'm just basing this observation from buying and selling them on the EBay market for the last several years.
Also, in the past (we're talking over 30 years ago), as the user above me mentioned, the former Department of Traffic used to have public auctions if old signs retired. The folks used to auction old traffic signal equipment as well.
Fast forward to 2015, and times have changed. Unless you know someone in the industry, the D.O.T. technically cannot take down a sign and give it to someone. It must be scrapped. The main reason is that it cannot be put up once again on an actual street corner, which is illegal. This is primarily why the NYCDOT sign store manufactures replicas of NYC signs single-sided rather than double-sided.