A badge with a multicoloured (but largely blue toned) background with a spray paint effect. Over top there is black text that reads "I still don't want kids. You don't need to keep checking, thanks".
If this is the first time you've realised it's a really damn invasive question, keep that. Remember that. It's a really damn invasive question. Stop it.
These badges are 37mm by 37mm square with rounded edges (photographed next to a 5p which is roughly the same size as a US dime to show scale) and will have a sturdy metal pin back. They're super durable (I've even put mine in the wash by mistake and it survived, though I wouldn't recommend it).