What sign in chart represents sexuality?

They all contribute just a tad somehow, but there are major ones :)
Moon is emotions and needs in bed, how you feel comfortable and how you trust.
Venus is affection and touching. The actual cheesy part of the scenario and lovey dovey part. Pay attention to this with the girls.
Mars is the movement, the 'kinky' and the aggression. I would say pay attention to this a lot with the guys.
Jupiter is expansion and growth, so if that is all good you could see how that might help. Especially if it is affecting mars and or venus.
Neptune is fantasies
Pluto is secretive and intense. Remember though that an entire generation has this same planet in them.

If you're also interested look at house placements in the natal chart as well :)
5th house is fun and sex
7th house is partnership
8th house is secretive and intense again like pluto

I think it is Venus and Mars.

I've noticed any aspects between
Pluto and Venus
Mars and Venus
Are there any signs in Scorpio? Scorpio can influence planets in a mysterious, secretive and sexual kind of way.
Black Moon Lilith

There is a lot others.. have you tried googling your question?

Mars and Venus

mars

Venus

Sign In Chart

The Sun (The Planet of Life force, ego, spirit, soul, vitality, creativity, the conscious self, and willpower) The Moon (The Planet of Emotions, instinctual reactions, memory, dreams, the unconscious self, imagination, and nurturing instinct) Mercury (The Planet of Communication, reason, logic, speech, mental energy, information, mental/physical skills, coordination, and dexterity) Venus (The Planet of Beauty, love, pleasure, eroticism, sensuality, luxury, money, the arts, values, attraction, and personal magnetism) Mars (The Planet of Energy, assertion, impulses, courage, daring, risk, action, confrontation, aggression, lust, and primal urges) Jupiter (The Planet of Expansion, personal growth, principles, wealth, higher power, humor, celebration, extravagance, and luck) Saturn (The Planet of Restriction, discipline, regulation, structure, stability, authority, age, time, karma, preservation, conservatism, and tradition) Uranus (The Planet of Change, surprises, revolution, awakenings, invention, modernity, science, electricity, and difference) Neptune (The Planet of Illusion, mysticism, spirituality, intuition, inspiration, impressionism, artistry, and mercy) Pluto (The Planet of Transformation, mutation, transmutation, destruction, obliteration, elimination, upheaval, regeneration, rebirth, renewal, power, extremes, and desires) Hope this helps!

seventh and twelth house owners and the planet venus

Astrology is meaningless. Never be fooled by it.