Carstens almost always used a red clay and marks were embossed rather than incised. Many items have the Carstens twin house logo which allows for easy identification.
If there was limited space on the base Carstens would often abbreviate Germany to “Germ” or “Germa” this is unusual amongst manufacturers but not unique to Carstens.
A number of Carstens items can still be found which retain their original labels. In some cases these can be used to provide an indication of when a vase was produced. Some are also found with original retailer/shop stickers.