Personally I don't think it is Murano. Rotating the image of the base 180degrees shows an impressed O. C. ?. where the ? is a letter I can not make out but you may be able to decipher. For whatever reason I am assuming they are the markings of an American studio. They are quite unusual in that I assume the base has subsequently ground flat so they must hyave been quite deep.
Sorry I can't be of more help.