Hi,
Since I do not see a separate town letter mark, the correct dating is 1872-1922.
During that period there were a few Austrian silversmiths with HE initials.
Among them there was a Heinrich Josef Ecker, active 1868-1908.
Maybe it was him, maybe not.
Regards,
G.
Inside the Diana mark there should be the cypher 3 (to the left, meaning the silver proof 800/1000), as well as a letter (to the right) denoting the assay office location (eg. A for Vienna). You may clean the mark and look for the letter with magnifying glass.