What you may refer to as "my sign" is really the zodiac sign in which the Sun was positioned at the time of your birth, according to the map of the heavens we call your birth horoscope or "birth chart". Astrologers call this your Sun Sign. Others may call it your "star sign". Your personal birth horoscope (birth chart) also contains the Moon and eight Planets, not just the Sun. Each of these were positioned in some zodiac sign at the instant you were born - and they indicate things about you that are not indicated by your Sun Sign alone!
In determining which other Sun Signs are most compatible with your Sun Sign, an astrologer looks at the "aspects" (which are just angles like 0, 30, 60, 90, 120, 150, or 180 degrees) which the Sun in those other signs would be making to your Sun in its sign. If the Sun is in the same sign or is making what are called "easy aspects" (60 and 120 degrees) to your Sun, then the Sun in that sign is easily compatible with your Sun Sign - and those are the ones shown in the Table above. Although it is not an "easy" aspect, I have also included the 180-degree aspect (Sun in the opposite sign) because these pairs of signs are "complementary" (meaning they "complete" each other), and because "opposites attract".
But there is much more to astrological compatibility than comparing Sun Signs alone. In the technique called "synastry", the aspects (angles) the Moon in your birth chart makes to the Sun in another person's birth chart are also very important, as are the aspects from their Moon to your Sun. And in romantic relationships, the aspects between your Venus and their Mars, and their Venus and your Mars, are of great significance. So don't judge a potential partner or friend as "incompatible" with you just because their Sun Sign does not show up as compatible with your Sun Sign in the Love Match table above, for there is much more to consider! Sometimes people with "incompatible" Sun Signs can have many compatible aspects involving their Moons and other Planets, and could be potentially great friends or partners, in spite of a Sun Sign incompatibility. See
Compatible Signs 2.