Why YSK: There are a lot of people these days living alone with pets and if anything happened to the owner, others may not know to attend to the pet. If something happened to you, a coma, an accident, death, etc, your wallet would be the first place anyone would look for info about you and it would probably be the fastest way to bring attention to your small loved ones.
They also make windows tickers that say “in case of emergency we have xyz pets”. Good to stick one next to the front door.