A valid digital signature gives a recipient reason to believe that the message was created by a known sender (authentication), that the sender cannot deny having sent the message (non-repudiation), and that the message was not altered in transit (integrity).
Load index is an assigned number that corresponds with the load-carrying capacity of a tire. Most passenger car tire load indexes range from 75 to 100, but a few carry more. You'll also find the maximum load elsewhere on the tire sidewall, both in lbs and kg.
LT: Designates that this is a Light Truck tire. Load index and speed rating are sometimes not mandatory for flotation sizes, but must be for any tire approved for street and highway use. 2- or 3-digit number: Load index; see table below. 1- or 2-digit/letter combination: Speed rating; see table below.