I just got the following from a SETI@home mailinglist:

---------- Forwarded message ----------
>Date: Tue, 6 Jul 1999 09:27:30 +0100
>From: (removed to protect the innocent)
>Subject: Careful now....

All of you American SETI participants should maybe be hoping you
_don't_ find anything, at least if the following is true. I got it
from a friend years ago and found it by accident again yesterday :-

Title 14, Section 1211 of the Code of Federal Regulations, adopted on
July 16, 1969, makes it illegal for US citizens to have an encounter
with extra-terrestrials or their vehicles. Those found guilty of such
an encounter face quarantine (with or without a hearing), up to a year
in prison, and a fine of $5,000.

[Note - reportedly an urban legend - ed.]