I am working on an app and want to name it Vidmark. Apparently, this name is the name of a long-defunct company (since 2001). Could I get into trouble using this name?
The answer is almost assuredly, no, you can't use it.
Vidmark was parented as Trimark Holdings which was bought by Lionsgate in 2001. Lionsgate is still very much an active company, and has been using the Vidmark name as lately as 2017 when it released a Roku streaming channel under the "Vidmark" name.
So Lionsgate is the holder of this particular trademark, and is actively using it.
TESS shows that the trademark is still Live and was re-registered in 2017.