Why Does Hooke's Law Use a Negative Sign in Scalar Form?

[Herman Trivilino]

And then there is the recurrent question, "if I substitute numbers for g in the equation, do I use +9.8 m/s² or -9.8 m/s² ?"

Years ago I was using a textbook that forced the students to make that choice. In other words, $g=\pm 9.8 \ \mathrm{m/s^2}$. That was a huge mistake.