I've also long used a string followed
by a colon in the subject line in various
situations (ie. "Q:") and never perceived a problem.

The problem would be percieved by others.

BTW, whats' wrong with displayed threading by threads instead of subject?

Nothing, but there's something wrong with having to. Sorting gets
screwed up in some readers when one must sort by threads if one is only
viewing unread messages.

Jose
--
There are two kinds of people in the world. Those that just want to
know what button to push, and those that want to know what happens when
they push the button.
for Email, make the obvious change in the address.