Two sections of Title 17 (Copyrights) are relevant. 17 USC 512 (safe harbor) and 17 USC 1201 (anti-circumvention). The notice is styled as one under 17 USC 512:

It has come to our attention that the web site www.brandonw.net, contains material and/or links to material that violate the anti-circumvention provisions of the Digital Millennium Copyright Act ("DMCA"). This letter is to notify you, in accordance with the provisions of the DMCA, of these unlawful activities. Pursuant to the safe harbor provisions of the DMCA, we request that you remove any whole or partial reproductions of and/or disable links to the following:

...

I hereby confirm that I have a good faith belief that use of the Illegal Material in the manner complained of in this letter is not authorized by the copyright owner, its agent, or the law, that the information in this letter is accurate, and that, under penalty of perjury, I am authorized to act on behalf of TI, the owner of the exclusive rights in the TI-83 Plus operating system software that are allegedly misappropriated using unlawful methods.

TI appears to be claiming that the copyright in the TI-83 Plus operating system software is infringing. This therefore appears to be a notice under 512(c)(3). Anti-circumvention is a totally different section of the copyright code, 1201. There is no takedown procedure for access control circumvention materials.

But with regards to anti-circumvention claims: It appears that TI is claiming that the signing keys circumvent a "technological measure that effectively controls access to a work protected under this title." This is a term of art.

(A) to "circumvent a technological measure" means to descramble a scrambled work, to decrypt an encrypted work, or otherwise to avoid, bypass, remove, deactivate, or impair a technological measure, without the authority of the copyright owner; and

(B) a technological measure "effectively controls access to a work" if the measure, in the ordinary course of its operation, requires the application of information, or a process or a treatment, with the authority of the copyright owner, to gain access to the work.

Are signing keys necessary to gain access to the TI 83 Plus operating system binary? As far as I know, no. My understanding is that they are only used to prepare operating system images for installation onto the calculator.

It's highly unlikely that the factors of an RSA private key are subject to copyright protection. Therefore the groups may have a viable claim for DMCA misrepresentation under subsection (f):

(f) MISREPRESENTATIONS- Any person who knowingly materially misrepresents under this section--
    (1) that material or activity is infringing, or
    (2) that material or activity was removed or disabled by mistake or misidentification,
shall be liable for any damages, including costs and attorneys' fees, incurred by the alleged infringer, by any copyright owner or copyright owner's authorized licensee, or by a service provider, who is injured by such misrepresentation, as the result of the service provider relying upon such misrepresentation in removing or disabling access to the material or activity claimed to be infringing, or in replacing the removed material or ceasing to disable access to it.

Texas Instruments may just have Diebolded itself.

Verizon math alert!

Because property owners would never increase their rents to cover the high taxes.

Landlords will charge tenants as high of a rent as the market will bear (tenants are willing to pay). They aren't cutting you any breaks. If their expenses go up, their profit goes down. If unemployment goes up, rents go down.

Anyway, property taxes are already everywhere.

The land value tax is not the same as a property tax, because it does not create a disincentive to invest in creating new property. You can build as many units as you want on a piece of land, and the tax remains the same.

A land value tax does distort market mechanisms.

But then you inadvertently point out how it aids a market mechanism:

The most obvious effect is that if many parcels in an area are improved, the value of the unimproved parcels is likely to go up, often considerably.

That's kind of the point. Unimproved parcels are being used inefficiently. It is better for this unused resource to go to a new, more efficient user. That's a market mechanism that is aided by the imposition of the tax.

1. It's something libertarians and socialists can both agree on.

2. It does not deter production or distort market mechanisms.

3. It's voluntary. Renters don't pay a dime.

Take a look.