What word can mean both signify and ignoble?
One word which can signify either "signify" or "ignoble" is "base."
As "signify": "Base" may mean something basic or foundational, such as "the base of an argument" or "the base of a building." It signifies the beginning or the underlying foundation.
As "ignoble": "Base" also signifies morally low, dishonorable, or of poor quality, such as in "base motives" or "a base character."