I personally tested the viability of using the window cling decals on an outdoor surface – my vehicle side window.
It is very important the glass surface is cleaned. I used only water and my shirt to wipe away the dirt, I recommend using glass cleaner.
I recommend you follow the instructions in this video for best methods of outdoor application.
Originally installed in early April 2019:
These two clings have endured speeds in excess of 70 mph, sun, rain, and snow…
After about 2 months, I believe these have held up quite well. There is are “less-clingy” parts, but I believe this is due to my poor glass cleaning.
I took the April clings off. they were about 1/2 off already. I will apply a new one properly and document the success/shortcomings of them on my vehicle exterior glass (which should be posted below when I get to it).