Board Thread:Q & A/@comment-73.160.228.159-20150212051037/@comment-26322846-20150418024212

Not always. There are two types of woges, one anyone can see, and one only Grimm and other Wesen can see. That being said, with a lot of disiciple a woge can be supressed. Most Wesen involuntarily woge in the presence of a Grimm, but for the most part they will try to keep their true natures hidden from other Wesen as it's hard to know how to kill a Wesen if you don't know what it is.

There are also some rather extraordinary circumstances, such as Folterseele, which only seem to woge as a defensive measure, mostly to ward off unwanted advances.