Halfcrowns bearing the letters "SA" may signify Salopia, the Latin name for Shrewsbury. In July 1643 Thomas Bushell's plans to re-open the mint at Shrewsbury had progressed to sending men to prepare the furnaces, so Shrewsbury is a viable candidate for the SA coinage.
During the English Civil War, the town was a Royalist stronghold and only fell to Parliament forces after they were let in by a parliamentarian sympathiser at the St Mary's Water Gate (now also known as Traitor's Gate). After Thomas Mytton captured Shrewsbury in February 1645; in following with the ordnance of no quarter; a dozen Irish prisoners were selected to be killed after picking lots. This prompted Prince Rupert to respond by executing Parliamentarian prisoners in Oswestry.
The 1644 coins covered here are Spink numbers 3119-3128, only some are inscribed SA; for the 1642 issues please click here.