There are several abrev. including: "^2 and in^2
1)Inna is a Russian name meaning "strong water" It was the name of an early male Russian martyr, but is currently used as a feminine name only... 2)Inna stand for Florentina and is a romanian abrev.
Google found it here. But also try pet shop (used for some aquarium treatments) or perhaps hardware shop: http://www.abchomeopathy.com/shop.php?search=&abrev=Metb&country=Hylands&Submit.x=84&Submit.y=9