Watch List notes:

Charles II (1660-85), Sixpence, 1678 over 7, laureate and draped bust right, rev. crowned shields cruciform, five strings to harp, cyphers in angles (ESC 573 (1517); S.3882), attractive lustre under old cabinet tone, haymarks on reverse, about extremely fine.
Maurice Bull ESC 573 notes the g of mag over o or d? There is clearly something underneath, but possibly the letter g has been double punched. Also, he notes only three harp strings, while on this coin there are clearly five.
Estimate: £200 - £300