Volovich states in P-adic Analysis and Mathematical Physics (pages 54, 55) that the following function:
$$\lambda_p(a) = \begin{cases}1 & v_p(a) \mbox{ is even} \\ \Bigl(\frac{a_0}p \Bigr) & v_p(a) \mbox{ is odd and } p \equiv 1 \mod 4 \\ i \Bigl(\frac{a_0}p \Bigr) & v_p(a) \mbox{ is odd and } p \equiv 3 \mod 4 \end{cases}$$
is of great importance but refuses to name it implicitly. $\Bigl(\frac ab\Bigr)$ denotes the Legendre symbol and $v_p$ is the $p$-adic valuation. What is its name?
Here $a = p^n(a_0 + a_1p + a_2p^2+ \ldots)$ is a $p$-adic number.