It appears that the insync-1.3.16.36155-fc25.x86_64.rpm package is missing its signature:
$ rpm -qpi insync-1.3.16.36155-fc25.x86_64.rpm
Name : insync
Version : 1.3.16.36155
Release : fc25
Architecture: x86_64
Install Date: (not installed)
Group : Applications/Internet
Size : 218480585
License : unknown
Signature : (none)
Source RPM : insync-1.3.16.36155-fc25.src.rpm
Build Date : Wed 26 Apr 2017 10:49:25 BST
Build Host : 79db519299fc
Relocations : /
Packager : Luis Manuel R. Pugoy lpugoy@insynchq.com
Vendor : @79db519299fc
URL : http://www.insynchq.com
Summary : Google Drive sync and backup with multiple account support