Hi,
Thanks for posting.
The only way you can do this is by turning off the 'Instrument Output Assembly' setting for your test projects. In this way, code coverage will not be tracked for source files in these projects.
However, there is a trade-off to this. NCrunch's impact detection requires instrumentation to work correctly, so if you turn it off for your test project, you won't be able to use the 'Run impacted tests only' mode.
Generally, it's better to leave them on. The markers are as useful in test code as they are in production code.