No company letter designation used. As Rick mentioned, an artillery battery is a company. In Confederate service, customary practice referred to a battery by name of commander. This meant that even when an artillery organization such as a regiment or battalion had recognized letter designations, companies were usually referred to by names of battery commanders.

In this case, the company entered service as Smith's Mississippi Battery. After Smith received a promotion and left the command, the battery became known as Turner's.

A note about the surrender:
When the surrender took place the record reads as if Maples was at Citronelle AL. "He was surrendered at Cironelle AL, May 4, 1865."

While technically accurate, the only Confederates actually present when the surrender agreement was signed were General Richard Taylor, a staff officer and two slaves. This group of four took a railroad handcar to meet General Canby at Citronelle. After Taylor's return, soldiers in camp at Meridian, Columbus and Gainesville AL were informed of the surrender. Starting on May 9, 1865, Taylor gave orders for each brigade, regiment, battery and detachment stack arms and receive paroles from Federal officers. Soldiers not present with their commands could go to a Federal military post and recieve a parole, which Maples evidently did at a later date.

Under Federal military guidelines, a Confederate soldier without a parole could be taken from his home and arrested. Don't know of any cases in which that happened, but men whose actual connection to the Confederate army was suspect were considered guerillas and treated as such. Federal reports from the Spring of 1865 mention hunting guerillas and summary executions. A parole was usually sufficient to prevent that from happening, although in at least one case a guerilla who was never in Confederate service received a parole as a Confederate staff officer. This may have helped him escape arrest and trial by Federal authorities. However, he killed his share of Southern civilians and Confederate soldiers, too. In 1868 someone caught up with the man in Parker County TX and brought an end to his career.