This is not very detailed but it might help: https://blog.adilparvez.com/post/2016/10/31/1/cyanogenmustar...
Isn't that a good way to get a modified / malware version of Signal? Anyone can upload to APKMirror, can't they?
This is also useful: http://www.onyxbits.de/raccoon It's a dektop play store client. I tried it out a while back and it worked, don't know about now.