Ye olde thorn

Thorn is a letter in the Anglo-Saxon and Icelandic alphabets. It represented the sound of the "th" in modern English. The original form used above lost its ascender and by the mid-15th century was indistinguishable from the letter "Y." So all of the older documents, signs and etc. that have the word "Ye" such as "Ye olde ..." are really saying "The." Use of the thorn is common in older documents but disappears around the middle of the 1800s. From Wikipedia, here is a list of the most common forms of the letter:

• (þ^e) a Middle English abbreviation for the word the
• (þ^t) a Middle English abbreviation for the word that
• (þ^u) a rare Middle English abbreviation for the word thou (which was written early on as þu or þou)
• (y^s) an Early Modern English abbreviation for the word this
• (y^e) an Early Modern English abbreviation for the word the
• (y^t) an Early Modern English abbreviation for the word that

Except for very fake advertising, the only modern real use of the letter is in Icelandic:

The Icelandic language is the only living language to retain the letter thorn (in Icelandic; þorn, pronounced þoddn, [θ̠ɔtn̥]) in common usage. The letter is the 30th in the Icelandic alphabet and never appears at the end of a word. Its pronunciation has not varied much, but in earlier times time þorn was sometimes used instead of ð as in the word "verþa" which is verða (meaning "to become") in modern Icelandic. Wikipedia.

Recognizing the use of the thorn is one of the minor issues in reading ye olde documents.