Just got this error when trying to do a ClickOnce publish to a UNC path on a new installation on Visual Studio 2015, "An error occurred while signing: SignTool.exe was not found at path C:\Program Files (x86)\Microsoft SDKs\Windows\v7.0A\bin\signtool.exe.".
Seems I'd forgotten to install the "ClickOne Publishing Tools", which is an easy fix.
Control Panel > Programs > Programs and Features > Visual Studio 2015 > Right-click "Change" > Modify > ClickOne Publishing Tools...
