I have written about the special headdress of dragoons here before. Then I presented a patriotic badge that shaped the helmet. The dragoon helmet also appeared on some regimental badges. It can be seen, for example, on two badges of the 15th dragoon regiment.
The helmet is the central theme of the plate badge with a simpler design. Above it is the abbreviation of the motto: “Austriae est imperare orbi universo”. It was the motto of the Holy Roman Emperor Frederick III, from whom it was later passed on to the entire House of Habsburg. Meaning: “Everything on earth is a subject of Austria”. This became the motto of the Theresianum Military Academy, founded in 1751 too. The badge referrers to this most probably. In any case, there are still debates about the interpretation of the abbreviation.
On the wearing photo we see a dragoon who could belong to the 15th regiment as well. We do not know exactly.