We removed the physical geodatabase relationships between poles and signs because we're relating multiple tables (signs, lights, signals) in the geodatabase to a single pole feature class. As such, we'd instead suggest you do a map join in ArcMap before you publish the service so you don't see all three features (signals, signs, and lights) in your service.
If you're interested in using AGOL and the Collector to tackle a sign inventory project, you'll have to flatten out the structure a bit more and essentially collapse the pole feature class and sign table in to a single Sign feature class. The Collector app does not support related tables at this time.
This workflow will work really well for your sign inventory, but won't help you with subsequent inspection workflows. The best solution right now if you want to use AGOL and the Collector app for ongoing inspections is to create a SignInspection feature class and capture point features for each inspection activity.
Scott