Well, these days it's a tiny piece of paper that signifies I can work in the US. But when I first got it at 3 years old, it said that I wasn't allowed to.
Makes sense if you're a child, but that's not the reason it said that - my mum's said it as well. It's an ~immigration~ thing. Only my dad was allowed to work for the 13 or so years we were stuck in visa purgatory.
Now that I think about it, it's possible it was supposed to be updated when I became a permanent resident, but I have a vague memory of applying for my first job with a Social Security card that said "NOT VALID FOR EMPLOYMENT" underneath my mum's signature. Oops?
It did eventually get updated when I became a citizen, over 20 years after moving to the States. While I did delay a couple years at the end, I'm still kinda bitter at how long the process takes. 22 years of, "if you fuck up somehow, you can be deported from the only home you can remember."