♊ (Gemini) is the third astrological sign in the Western zodiac, ruled by the planet Mercury. The sun is in this sign between 21 May and 20 June. Some of the coolest people out there were born under this sign. They are often referred to as “Geminis”, for no good reason. As the word “Gemini” is derived from Latin geminī, which is already plural of geminus (“twin”), there no need in further pluralisation.
The glyph ♊ looks like a variant of the Roman numeral Ⅱ, which it most probably is.