According to Wikipedia, there are at least 35 letters on hillsides in Idaho, and maybe as many as 42. Most of them are the first letter of the town’s name, or a letter representing a local high school sports team. Franklin, the first town founded in Idaho Territory, has its big F, but above that are the numerals 1860 for the year it was founded.
Pocatello had a big concrete I on Red Hill representing Idaho State University for many years. It was placed there in 1927. Travelers going south on I-15 knew it as a Pocatello landmark. But in 2014 it was removed because of the risk of a hillside collapse due to heavy erosion. The fear was that the concrete initial might come crashing down on trail users below.
In the book Quintessential Boise, An Architectural Journey, by Charles Hummel, Tim Woodward, and others, they say the B on Table Rock above the Old Idaho Penitentiary, was placed there in 1931 by Ward Rolfe, Bob Krummes, Kenneth Robertson, and Simeon Coonrood, who were proud graduates of Boise High. As is the case with many such letters, the rocks often get a coat of paint to make them stand out.
Does your town have a letter? Post a picture in the comments section so we can all get a look. Do you have a story that goes along with the letter? An artifact of aliens, perhaps, or the site of your wedding proposal. Please share that, too.