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 load index value for most truck tires will fall between 109 and 130 (2,271 pounds to 4,190 pounds, respectively). However, keep in mind that a tire with a load index at the low end of that spectrum and one with say, a 126 value, can both be E-rated. A great load index chart is available at discounttire.com.