In any circumsatance, they can not copyright the using of "Watchtower" (like in "Watchtower Observer" or "Quotes-Watchower") for the term "Watchtower in not for themselves. That's what they themselves wrote in the Proclaim book (WTS 1993, page 48, footnote):
"The expression "Watch Tower" is not unique to Russelll's writings or to Jehovah's Witnesses. George Storrs published a book in 1850's called The Watch Tower: Or, Man in Death; and the Hope for a Future Life. The name was also incorporated in the title of various religious periodicals. It stems from the idea of keeping on the watch for the outworking of God's purposes._Isa.21:8,11,12;Ezek. 3:17;Hab. 2:1." (quote from "Proclaim book, page 48, footnote)
And a couple of Mormons and Adventists "periodicals" had the same name
Here: http://www.lavazone2.com/dbroadhu/NY/MiscNYSE.htm#013131
Here http://www.geocities.com/le_thanh_y/W_SDA.jpg
In addition, if you use google serch engine and type "Watchtower," you will find out heaps of companies take this "Watchtower" name. Do they sue all of those companies ?
jwsons