The 1880 Sydney crenulated reverse half sovereign is a rare subset of the 1880 which features a toothed or crenulated reverse rimas opposed to the standard beaded type. It was struck at the Sydney mint as denoted by the S mintmark under the shield. One should be careful not to confuse the S with a 3 or 8 die number which were sometimes used by the Royal mint London.
The 1880 Sydney with the crenulated reverse rim is the scarcer of the two varieties though at the AU level or in mint state there are a disproportionately high number of surviving examples making the issue seemingly more common in higher grades. Despite this, the variety's rarity has kept prices strong in the higher grades.