Sign sounds like a good idea. But if I was a bystander, I'd want to be sure any animal was in real distress before I damaged real property. That is a crime independent of motive.
On another thread, someone posted that step one is locking car from inside first (which I had posted) was not necessary, and that using the mechanical key will lock all doors. I haven't tried to confirm that myself as I'll never need to do that but I had tried it your way and it worked.
2018 Kia LX HEV Metal Stream with Advanced Tech