For a formula $\varphi(x_1,\dotsc,x_k)$ and an integer $n$ we define $R_\varphi(n)$ to be the least integer $N$ such that every sequence of length $N$ contains a $\varphi$-indiscernible subsequence of length $n$. In this talk we discuss the growth rate of the function $R_\varphi$ in o-minimal structures over the reals and other NIP structures.