Perhaps the ultimate demonstration of a company's faith in its product is how strongly it is willing to warranty it. Arai was the first to offer a full 5-year warranty, and still does on all their helmets.
"All Arai helmets are warranted against defects in materials and workmanship, and as serviceable only for the properly-fitted first user for 5 years of use, but no more than 7 years from date of manufacture. It should be replaced within 5 years of first use."
The Warranty is stamped on one side of the leather portion of the chinstrap (one of the chinstraps is shown in the photo below). The date-of-manufacture (month / year) is stamped on the opposite strap.