The signature, or technical the Chinese characters are the artists name.
It means South Field which in mandarin is pronounced Nan Tian.
The red stamp at the bottom, or chop in Chinese, is Nan Tian again. Look at the similarities.
Typical Chinese names are three characters but in the case of this watercolor there is only two.
When I lived in China I would sign correspondence with my handwritten Chinese name and then use my chop which was used with a red ink pad to stamp my name as well.