What sign is compatible with Ophiuchus?

Ophiuchus is not part of the traditional Zodiac. Although Scorpio is a very prominent constellation (in fact, one of the only ones that is even recognizable as what it is said to be), a lot of the stars lie well to the south of the line marked by the apparent path of the Sun and planets (the ecliptic). That didn't matter to the astrologers -- they called that sector of the sky after the dominant constellation.

Astronomers are a little more fussy, and they have established very fixed, rectilinear boundaries between the constellations, and, according to their reckoning, a segment of the ecliptic passes through the segment they label Ophiuchus. (And very little of the ecliptic passes through Scorpio.)

However, the astronomers' boundaries are completely irrelevant to astrologers; on top of which, most western astrologers don't even use a form of the Zodiac that lines up with the constellations.