Order yourself Some old school temporary tattoos. I got these from China, via eBay but you could also check out somewhere like rosie wonders.
Roughly cut out your design and have a go and looking where it will sit best.
Use a wet cloth to soak the back of the paper. Don't be shy, get it wet.
The backing will slide away. Like magic.
And that's all there is to it! I've had mine on my bag for quite a while now and they wear well.
Let me know if you give it a go!