Colour symmetry in the same pattern. Yellow lines are the border of a fundamental region. Small circles mean rotations; numbers mean rotations of order 2 and 4. Mirrors are represented by red lines. Glide reflections are not represented. (12) means that the colours white and green are interchanged; i means the identity.
This is an example of the case stated in the fourth row of the table in Section 4.11 (Figure 15, «p4gm») in
Wallpaper groups. Tiles: Portugal, Palácio Nacional de Sintra - c2mm
Azulejos do Palácio Nacional de Sintra / Sintra National Palace Tiles