[GeronL]

I am going to copyright the letter T!

[FredZarguna]

Too late: The Letters A-Z®, NUMBERS 0-9® [and all combinations including decimals], plus the Greek Letters α through ω® are registered trademarks of Frederick Jasper Zarguna. All rights reserved.

[Swordmaker]

I am going to copyright the letter T!

Believe it or not, you actually can, so long as it is part of the design of a typeface you've completely created from scratch. You are allowed to copyright the alphanumeric letters and numbers, symbols, etc, and control the use, licensing, of all versions of those letters in that typeface. . . and sue people who use it without permission!

Check what Adobe charges for the use of their typeface libraries, the complete set is something like $650, and more, if you actually print a large print run of a book.

[xp38]

T? Piker! Go for e which is the most commonly used letter in english and you get royalties from the calculus crowd too.