There are two scenarios — initial setup pairing and pairing a physical remote after setup via the mobile app. Here's both:
Initial Setup (out of the box)
Press and hold the Home button on the remote until "Press button to start" appears on screen — about 10 seconds. The remote is now paired and ready to use for setup.
Adding a Physical Remote After Setup (via the mobile app)
If the Stick was already set up using the Amazon Signage mobile app and you want to add/re-pair a physical remote:
With your Signage Stick powered on and connected to a screen, launch the mobile app.
Launch the virtual remote for your Stick.
Tap the Settings button (gear icon) on the virtual remote — your screen should switch to a Settings menu.
Navigate to Connected Devices using the virtual remote's arrow and OK buttons.
On the physical remote, press and hold the Home button until you see a flashing orange light.
Using the virtual remote, navigate to "Pair new device" and select "Amazon Fire TV Remote" — the physical remote should now be paired.
If the screen becomes unresponsive to the virtual remote during this process, close the mobile app and reopen it.
One thing to note: after initial setup, the Signage Stick restricts use of the Back and Home buttons on the remote to prevent the device from exiting kiosk mode. The Settings button remains available to change Wi-Fi and other settings. Also, Alexa and App buttons are disabled on remotes paired to Signage Sticks.