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.
The first two digits (87S) represent the tire's load index and are followed by a single letter (87S) identifying the tire's speed rating. Using a P195/60R15 87S tire size as our example, the 87S at the end of the size represents the tire's service description.