Is it a crime to use the presidential seal in a joke?  I want to send
a friend a letter "from the President," and I want to use the
presidential seal on the envelope, in the return address area.

I'm sorry to be the bearer of bad tidings, but in the current climate
of federal law enforcement, and in view of this section of the U.S.
Code, I suggest that you reconsider your plans.

"Whoever, except as authorized under regulations promulgated by the
President and published in the Federal Register, knowingly
manufactures, reproduces, sells, or purchases for resale, either
separately or appended to any article manufactured or sold, any
likeness of the seals of the President or Vice President, or any
substantial part thereof, except for manufacture or sale of the
article for the official use of the Government of the United States,
shall be fined under this title or imprisoned not more than six
months, or both."

Cornell Legal Information Institute: U.S. Code
http://www4.law.cornell.edu/uscode/18/713.html

Even a parody of the Presidential Seal could be risky, as in the case
mentioned in this interesting article:

"The White House attorney also told [John] Wooden that he couldn't use
the presidential seal, even though the seal on WhiteHouse.org has a
vulture in the center of it, rather than an American eagle...

BUZZFLASH: Overlooked in the coverage of the letter from the vice
president's lawyer is that he also asked you not to use the
Presidential Seal, but the Presidential Seal on your site has a
vulture at the center of it instead of a bald eagle. What gives?

JOHN WOODEN: My question exactly. One would think that White House
employees in general -- but especially those in the Cracker Jack legal
department -- would be able to correctly differentiate between real
and spoof Presidential seals. Then again, you'd think they'd have
learned about the Bill of Rights, too."

BuzzFlash Interviews
http://www.buzzflash.com/interviews/03/03/14_wh.html

Google search strategy:

Google Web Search: "presidential seal" use likeness
://www.google.com/search?hl=en&ie=UTF-8&q=%22presidential+seal%22+use+likeness

I'm sure this is not what you wanted to hear, but I hope the
information is useful. If anything is unclear or incomplete, please
request clarification; I'll be glad to offer further assistance before
you rate my answer.

Best regards,
pinkfreud

Thank you.  That is exactly the information I needed.

Thanks for the five-star rating and the tip!

~pinkfreud

The law quoted seems to pertain to commercial use, but then again you
never know what to expect under the current repressive regime.

It's not just the current regime. During the Clinton years, a friend
of mine who operated a small diner received a "cease and desist" order
because he had laminated replicas of the Great Seal of the United
States onto the toilet seats in the restrooms. Apparently some
disgruntled customer wrote to Washington about this outrage.

Not being from the States I don't quite understand. Is the
Presidential seal something like the UK Queen's corgi dogs?