Integral of the Fourier spectrum?
If $x(t)$ and $X(f)$ are Fourier transform pairs then the value

$$\int_{-\infty}^{\infty}|X(f)|df$$

can serve as an upper bound on the magnitude of $x(t)$:

$$|x(t)|=\left|\int_{-\infty}^{\infty}X(f)e^{j2\pi f t}df\right|\le \int_{-\infty}^{\infty}|X(f)|df$$