The Obol was equivalent to an English halfpenny and was (after 1834) subdivided into 5 Lepta, so the Thirty Lepta coin was equal to three pennies and is listed as "Three Pence" in some sources.
Coins were minted at the Royal Mint in London and, unlike the rest of the Ionian coinage (or comparable British coinage for that matter), they display the value (but not denomination). Total mintage from 1848 through 1862 was 330,720; no mintage figures for individual years are available.
On some coins there is a dot after the date and on some there isn't. However, this doesn't seem to be a mint mark. According to Remick's Guide and Catalogue of British Commonwealth Coins, some of the Ionian coinage was struck at the Ralph Heaton and Sons mint in Birmingham, but there is no indication which. The Greek Wikipedia entry on Ionian coinage only shows Birmingham one Obol (five Lepta) coins.
Composition: 0.925 silver (0.0419 oz ASW).