What a travesty, yes it should have an EK in the middle .
I'm afraid I don't have one yet, but here is a scan of the 25 & 40 from Hüsken's catalogue. Please excuse the distorted shape of the 25, but I couldn't get the page flat...... The badge is round in the book
It's a 25yr membership badge for the NS Deutscher Marinebund (NSDMB), it also came in 40 & 50 Year versions.