Where is the sign up button?

Licaon_Kter:

Spam waves, registration is closed for now.

I hope this is not a permant solution because it would prevent new people from joining the community and therefore hampering F-Droid`s mission.

You could fix the spam by giving the user’s the option to either verify with a phone number or to pay a small registration fee (which would not only deter spammers but also help F-Droid), preferably also offer privacy and FLOSS friendly payment options like for example Bitcoin Lightning.