Jemand hat ein absolutes Halteverbot Schild für einen Tag auf meinem Privatparkplatz erteilt?

On a private basis, which belongs to you, this is not possible without your consent. But: Some construction companies and, unfortunately, also some authorities do not take this so accurately and consider the mandatory communication that the place will not be accessible due to any measures on public grounds, so you could neither go to the place nor leave it. In doubt, call the competent office (which is organised differently locally, usually the Road or Regulatory Office), which must approve such signs and should therefore know the background.