Based on standard capitalization rules, the "proper text" formatting for depends on its context, generally resulting in:
(If it is a model number, part number, or serial code, it is best written in all-caps, as numbers are considered neutral and letters in codes are usually capitalized for clarity). 68539x
If you can tell me what this code is for (a product part, a software variable, etc.), I can give you the exact formatting standard. Convert Text to Proper Case - Online Text Tools Based on standard capitalization rules, the "proper text"