Additional letters of support (no more than four) for the nomination from individuals knowledgeable of the nominee's contributions relative to one or more of the criteria stated above. (amte.net)
When all 5 words have been written, students place each word in the word search puzzle and add additional letters to fill in the boxes. (teachnet.com)
That is why you may see a flurry of additional letters after their names these days. (fortune.com)