Because Zodiac signs are a part of astrology, (not to be confused with astronomy, which is the scientific study of the universe) and the Bible says that astrology (which is based on a person's interpretation and meaning of what they read into while they observe), is considered evil, we know it displeases God.

Does the Bible forbid astrology?

“The truth is that the Old Testament does speak against a large number of occult arts (e.g., Ex 22:18; Deut 18:10), but astrology is not among them,” notes Hard Sayings of the Bible.

Why is astrology wrong?

Astrology has been rejected by the scientific community as having no explanatory power for describing the universe. ... Astrology has not demonstrated its effectiveness in controlled studies and has no scientific validity, and is thus regarded as pseudoscience.