Currently there is no notification when a ride/run/activity is flagged – I just happened to be checking on a ride I did earlier in the week and noticed that it had been flagged by a user incorrectly (it wasn't an auto-flag as it only was flagged at some point after the day of upload). I know that in the past I have flagged other's rides weeks or months or even years after they were completed, and if I were that person I'd want to know when that happened so I could address it (cropping, making private, etc).
There is also no way to view which of your activities are flagged; the Strava blog does mention that a flagged ride would appear as red in the "My Activities" section, but that function is buggy or broken because this ride was not identified in the list view (only when clicking into the activity could I see the flag).
One of those two features is a must have; either a notification when your activity is flagged by a user or giving users a way to filter for their flagged rides in the "My Activities" section – as a long time user, I have close to 3000 activities and now I'm paranoid that I have some hidden flagged rides that I need to take care of buried somewhere in my long list of activities. But without one of these it's infeasible for me to stay on top of any flags in my activity history (or any new flags that come up).
I'm sure the filter in the "My Activities" section would be easier to implement, so I'd recommend that to start.