On a per show basis provide an option (default off) to automatically delete the recording if the signal error was above a threshold.
My PBS station quality varies and I record pbs kids shows off of it. For these situations it would be great to just let it try to record and then automatically trash the recording if it is of poor quality. Otherwise I have to just disable the channel entirely, giving up the times it comes in strong. If this is a per show setting then it could set on things that users would prefer not to keep if the signal was poor (maybe re-runs of shows that will be available for recording in the future) while leaving things they want to see even with poor signal alone (like live sports).