Sign vs House
A zodiac sign is the quality of energy: fiery, earthy, airy, watery, with its own character.
A house is the area of life where this energy lands: body, money, communication, home, creativity, work, relationships and so on.
A planet in a sign answers "how it acts". A planet in a house — "where it acts".
Example: Mars in Aries in the 10th house = combative initiative (Mars in Aries) playing out in career and public role (10th house).
The full natal picture is built on this intersection of signs, houses and aspects between planets.