Haha, that was funny. The reason why I think that invisible ink is riskier is that you have to write on paper with it and then keep this paper saved safe somewhere. You also need UV lights to see what's written. What if you are in a hurry and don't have access to UV lights? That's why I prefer a label tag on a t-shirt. It's knitted on the T-shirt with needle and fibre, it's not going to be lost and it's with you on your T-shirt. You can doff it anytime and restore your wallet.
No one is going to steal your t-shirt as you wear it. Btw don't wear Armani Exchange or Calvin Klein, that's a little riskier

What pros and cons do you see in both ideas? I would love to hear that from you too.