I my previous ISS, working with Inno Setup 5, I had the following command:
In the Sign Tools configuration I had a "signtool" entry only with the full path to the signtool.exe file. I was very convenient. because I could have a single signtool definition for many applications.
This no longer works with Inno Setup 6 (tested on 6.0.5 and 6.2.0), because SignTool directive doesn't pass any parameters to the signtool executable.