Sinister
A good few years ago, I typed the words "They know" in the middle of a sheet of paper, put it in a small unmarked envelope. When I next went round to a friend's house, I pushed it through the letterbox and then knocked on the door.

He answered, and noticed the envelope. He opened it and read the note. His first response was "What the fuck?"

He then went and swapped his hard-drive, ran a low level format of the old one and then hid it at the back of a cupboard.

I finally admitted it was me about 2 years later. He called me some names. He then told me about all the confidential files that he'd been bringing home from where he worked at the time.

I never did find out what he was planning to do with them..
( sandettie light vessel automatic New Twitter - @bollocksreally, Tue 2 Dec 2008, 10:57, 6 replies, latest was 16 years ago)

I reckon
If every single person got one of those letters, over half the world's population would destory evidence of some kind.
(GONEism, Tue 2 Dec 2008, 11:50, Reply)

Especially
if the government did it as a mailshot, one of those junk mail things that aren't addressed to anyone.
( sandettie light vessel automatic New Twitter - @bollocksreally, Tue 2 Dec 2008, 13:46, Reply)

Though it would depend on the font
If you used one that looked like it came out of a typewriter, you'd scare the living jism out of people.

If you used Comic Sans, on the other hand...
(LongJohnBaldry, Tue 2 Dec 2008, 13:52, Reply)

If you were a nonce
Comic Sans might be even more scary
(GONEism, Tue 2 Dec 2008, 14:17, Reply)

Even scarier:
use one of these.

(Safe for work)
( The Resident Loon Not a demographic. Do not measure., Tue 2 Dec 2008, 14:20, Reply)

Font
It was with a proper typewriter (not mechanical sadly), but it was certainly sinister. It would've been less scary if I'd have cut the words from a newspaper.
( sandettie light vessel automatic New Twitter - @bollocksreally, Tue 2 Dec 2008, 14:36, Reply)