The words yores, yours sound the same but have different meanings and spellings. Why do yores, yours sound the same even though they are completely different words?
The answer is simple: yores, yours are homophones of the English language.
Eye dialect spelling of yours.
Used to indicate the one or ones belonging to you: The larger boots are yours. If I can't find my book, I'll take yours.
Used often with an adverbial modifier in the complimentary close of a letter: Sincerely yours.
yours truly I, myself, or me: "Let me talk about a typical day in the life of yours truly” ( Robert A. Spivey).
Definitions from Wiktionary, Creative Commons Attribution/Share-Alike License, from The American Heritage® Dictionary of the English Language, 4th Edition and Wordnik.
Homophones (literally "same sound") are usually defined as words that share the same pronunciation, regardless of how they are spelled.
If they are spelled the same then they are also homographs (and homonyms); if they are spelled differently then they are also heterographs (literally "different writing").