What Should USA Citizens Know About Using Personalised Letters for 30-Day Tourist Visa Extensions in Thailand?

A USA citizen has received a 'personalised' letter from the USA embassy in Thailand for a second extension of their 30-day tourist visa. The letter includes their name, date of birth, and passport number. Although they still have time left on their first extension, they are uncertain about the effectiveness of the letter. Commenters suggest that while these letters are being issued, they should be printed in color and may not be accepted at all immigration offices.