MaakMijnldee's cat figure, see thing:35495, is asymmetric. A mirror reflection turns a right facing cat into a left facing cat that is not superimposable. I find it an attractive motif and suitable for representing the 17 plane groups.

Here are 4 coasters for dual extrusion which illustrate plane groups p1, p2, pm and pg. Constructed directly on the build surface they have pleasing smooth surfaces.

Four pairs of stl files are provided:

cat_coaster_p1.stl and cat_decoration_p1.stl
cat_coaster_p2.stl and cat_deocration_p2.stl
cat_coaster_pm.stl and cat_decoration_pm.stl
cat_coaster_pg.stl and cat_decoration_pg.stl

Cat_coasters_01 scad created the stl files and the images are in coasters_dxf_01.zip. Hopefully more will follow.

The coasters are 110 mm in diameter and should be constructed directly on the build surface. I used one shell and ten percent infill and the coasters printed in about two hours.

The coasters can be used as teaching aids. The four coasters illustrate 3 of the symmetry elements of the plane groups: reflection lines, glide lines, and 2 fold axes. Pdf files that show some of the symmetry elements are included in coasters_dxf_01.zip. Reflection lines are shown in red and glide lines in blue.