> 1. What is the best way to communicate issues to the pilot if you're a passenger and see something the pilot can't see?

Flight attendants is the passengers' interface to the whole flight environment. BTW there's seniority rank among the attendants too, chain of command, so to speak.

I would think that your observation was likely being noted, not sure if relayed to the pilots. Juice is the best option, noone needs to have a panic in the cabin.

Did you try to mention that observation again but at the arrival, during the "Thank you, good bye!" time? Sometimes you may even see the captain there.

P.S. Once, my flight was cancelled (all boarded already) because the crew discovered a missing "Exit" sign in the cabin and the mechanics at the airport could not find the exact part for the plane model. Call this an attention to details!