As I stated in my post, I'm trying to generate the signed URL from my channel. That's how signed URLs work... you need to create it from your program based on the current date/time and expiration time, server operation like GET, etc.
I'm not aware of any feature in the AWS S3 console UI for obtaining a presigned URL to a file. Such a URL that doesn't expire would essentially be the same as giving public access to the file if somebody finds the signed URL in my feeds.
I need somebody who's written a channel that accesses private AWS S3 files to tell me what BrightScript code they used to create the signed URL for providing to the Video component.