Luckily, in Poland, the law protects designers to a great extent. If you are able to prove that this other designer executed your idea on request from your ex-client, or somebody used your work without you giving them rights to do so, you can take it to court and it’s 90% chances you’ll win. The remuneration is few times higher that the salary you’d get, obviously This is a recent change, dating few years back and it has given designers so much room to breathe it feels weird as for an Eastern European country
But before these times, you’d have be extra careful. Sometimes, watermarking your designs wouldn’t help. So we’re really grateful for this update in law.