This domain is a subdomain within Microsoft's SignalR service, part of the Azure cloud platform. It returns a 403 Forbidden page, which is typical for internal service endpoints that are not meant for public browsing. The security checks come back clean: a valid TLS certificate issued by Microsoft, enforced HTTPS, and no malware or phishing flags from Google Web Risk. The hosting network is Microsoft's own, and the domain is not blacklisted anywhere.
Because this is an infrastructure endpoint, questions like "is sigr-relesyscore-prod-weu.service.signalr.net a scam" or "is sigr-relesyscore-prod-weu.service.signalr.net fake" don't really apply the same way they would for a consumer website. There's no attempt to impersonate a business or collect personal data. This is simply a backend service that powers real-time web features for applications using Azure SignalR. The lack of an about page, contact information, or social media presence is completely normal for this type of endpoint.
In short, this is a legitimate Microsoft Azure resource. If your application connects to it, it's safe. The signals all point to a trusted, well-maintained infrastructure component.