Tangential velocity signature for sources comoving with the cluster IC 2391 in Galactic projection. The top panel displays velocities along Galactic longitude (v_l), and the bottom panel shows velocities along Galactic latitude (v_b). The position of the cluster core is marked with a black star. The tangential velocities depict a complex, highly variable pattern and illustrate the challenge of identifying comoving populations in large regions of the sky.