The end of support for the legacy version of SignalScope Pro was announced in January of 2018. The final update was published in March, 2018, and the app was removed from sale on the App Store in July, 2018.
Faber Acoustical Releases SignalScope X for iOS as a Free Download
Current alternatives:
Free Download + Subscription:
SignalScope X
Perpetual License
SignalScope Pro 2018
SignalScope Advanced 2018
The Advanced Tool Set subscription in SignalScope X and SignalScope Advanced 2018 most closely match the functionality of the old SignalScope Pro.
Subscriptions are recommended for anyone who plans to always run SignalScope on the latest version of iOS.
Perpetual license versions are recommended for those who need to run SignalScope as a dedicated instrument. This means on a device dedicated for measurement/analysis/data acquisition that can continue to serve its purpose indefinitely without the need to upgrade iOS. (Of course, upgrading iOS is fine in this case, as long as it is supported by the perpetual license version of the app.)