Great question — answering as the UphillTech team:
Typically those would be installed in/with mortar or stucco, which would key into the depression in the back. That or construction adhesive would be the logical approach unless you want them removable and don't mind something like 3 stainless steel nails capturing it around the edge (mark, remove, drive two, place disk, drive the third with care) or 3 L hooks.
Full answer by Ecnerwal: https://diy.stackexchange.com/a/184156 (CC BY-SA 4.0).
Need it done for your business? UphillTech.
