Is the following statement true?
For all $n$ large enough, there exists an $M_n \in \{\pm 1\}^{n \times n}$ such that the smallest singular value of $M_n$, $\sigma_n(M_n) \gtrsim \sqrt{n}$.
If $n$ is such that there exists a Hadamard matrix of order $n$, we can take $M_n$ to be that.
It says here on Terry Tao's blog that "To oversimplify somewhat, the conclusion of this work is that the least singular value $\sigma_n(M_n)$ has size comparable to $1/\sqrt{n}$ with high probability."
This does not rule out the possibility that for all $n$ large enough, the random signed matrix $M_n$ satisfies $\sigma_n(M_n) \gtrsim \sqrt{n}$ with a tiny non-zero probability.