Where to Find and Catch Sigilyph
From Pokemon Go Wiki
Sigilyph are found and captured in Nest and Habitat locations.
Nests
Sigilyph Nests are locations that consistently spawn Sigilyph.
Habitats
Sigilyph Habitats are spawn locations where Sigilyph is likely to be encountered, but not guaranteed the way a Nest is.
Additional Tips and Information
Best Nests
If you know a really good nest or any of the nests above is really good, list them here: