Dear D P:

You wrote:

We are having a discussion. If we write a business letter and say “Dear Bart”, should we close the letter by signing in blue ink our given first name. (Our standard signature block is used with entire name typed.)
Good question. I guess it would depend somewhat on the relationship you have. Generally, nicknames would be used in memos. However, I do understand that sometimes it is important to personalize the business letter, and that a salutation with a nickname would be appropriate.

How you sign the letter would depend mostly on how the recipient addresses the writer. For example, my boss might address a letter to me as “Dear Jim” but since I always call him “Mr. Brown,” he would sign his full name. However, if we commonly addressed one another as “Bill” and “Jim,” then it would be appropriate for him sign the letter “Bill.”

If the person signing the letter is on a true first-name basis with Bart, then he should sign his first name or nickname. (I have known Barts whose full name is Bart, but I have also known Barts whose name is a nickname for Barton or Bartholomew.) If he is not, or if Bart calls him by a more formal name, then use the standard signature. In most cases, it is a question of formality vs. familiarity.

Having said that, some large corporations or government agencies always have the full signature regardless of the situation unless it is in a memo. If for some reason the letter could be used later in a legal situation, e.g. you are presenting Bart an estimate, then you should also sign your full name to show you mean business.

I hope this helps.